Post on 16-Mar-2020
transcript
November 7-9, 2019
DAE-BRNS Theme Meeting on Ultrafast SciencesRoom No-21, VMCC
We gratefully acknowledge the assistance and support of our sponsors and partners
Platinum Sponsors:
Diamond Sponsors:
Gold Sponsors:
3
Schedule
November 7
0830-0900 Registration
0900-0930 Inauguration. Chief Guest: Prof. Milind Atrey, Dean (R&D), IIT Bombay
0930-1010 Session 1: Plenary lecture 1: Chair: P. A. Naik
H. N. Ghosh “Exciton, Bi-Exciton, Trion and Polaron Dissociation Dynamics in
Nano-Structured Hetero Interface: Implication in Solar Devices”
1010-1040 High tea
1040-1230 Session 2: Invited Lectures (IL): Chair: S. K. Sarkar
IL 1: Vandana Sharma, “Transient Negative Polarizability Frustrates Alignment
in Ultrashort Laser Induced Fragmentation of Molecules”
IL 2: Jyotishman Dasgupta, “Elucidating the Transient Raman Signature of a
Twisted Intramolecular Charge Transfer State”
Session 3: Invited Lectures (IL): Chair: Rajib Mitra
IL 3: Jean C. Tremblay, “Probing Molecular Chirality via Laser-Induced
Electronic Fluxes”
IL 4: Sayan Bagchi, “Hydrocarbon Chain-Length Dependence of Solvation
Dynamics in Alcohol-Based Deep Eutectic Solvents: A 2D IR Spectroscopic
Investigation”
1230-1310 Session 4: Plenary Lecture 2 Chair: D. Goswami
K. Tominaga, “Hydrogen-Bond Dynamics of 9-Fluorenone Derivatives in Water
Probed by 2D-IR Spectroscopy”
1310-1400 Lunch
1400-1550 Session 5: Invited Lectures (IL): Chair: K. G. Suresh
IL 5: Mahesh Hariharan, “Ultrafast Excited State Dynamics of Twisted
Aromatics”
IL 6: Prasun Mandal, “Effect of Alloy-Shelling on Ultrafast Dynamics in
Semiconductor Quantum Dots”
Session 6: Invited Lectures (IL): Chair: S. Prabhu
IL 7: Anand Moorti, “Electron Acceleration using Laser Fields at Extreme
Intensities in Plasmas: An Advanced Accelerator Concept”
IL 8: K.P. Singh, “Ultrathin attosecond delay-lines with absolute zero delay
reference”
1550-1620 Tea
1620-1700 Session 7: Plenary Lecture 3: Chair: P. K. Datta
D. D. Sarma, “Experiments in the Sub-ps Regime to Understand Properties of
Opto-Electronic Materials”
1705-1815 Session 8: Technical talk 1: Anatech, Invited Lectures (IL): Chair: J. Jayabalan
IL9: Pankaj Mandal, “Probing the origin of self-trapped excitons in hybrid lead
halide perovskites using time-resolved spectroscopy”
IL 10: Sivarama Krishnan, “Opportunities in ultrafast science with laser
generated XUV pulses”
4
November 8
0930-1010 Session 9: Plenary Lecture 4: Chair: G. Dixit
S. Mukamel, “Nonlinear spectroscopy and imaging of molecules with x-ray,
quantum, and noisy light”
1015-1105 Session 10: Invited Lectures (IL): Chair: Suman K. Pal
IL11: Anshu Pandey, “Temporal Evolution of Radiative Rate Reveals the
Localization of Holes in CuInS2-based quantum dots”
IL12: Rajesh Kushwaha, “Photoionization of Polyatomic Molecules: Molecular
Structure, Ultrafast Dynamics and Molecular Movie”
1105-1135 Tea
1135-1215 Session 11: Plenary Lecture 5: Chair: T. K. Mukherjee
G. Ravindra Kumar, “Ultrafast Evolution of Dense, Hot Plasmas
Physics and Measurements in Extreme Conditions”
1220-1310 Session 12: Invited Lectures (IL): Chair: P. Sen
IL 13: Parinda Vasa, “Ultrafast Dyjnamics inMetal/Semiconductor
Nanostructures”
IL 14: Adam Kirrander, “Ultrafast X-ray Scattering of Molecular Dynamics”
1310-1400 Lunch
1400-1640 Poster + Tea
1640-1830 Session 13: Technical talk 2: Partha Pal, Wiley,
Invited Lectures (IL): Chair: P. Purkayastha
IL 15: Dipanshu Bansal, “Probing Lattice Instabilities in Thermoelectric SnSe
using Spectroscopic Studies”
IL 16: G. Naresh Patwari, “Intermolecular Tuning of Non-Adiabatic Dynamics
via Hydrogen Bonding”
November 9
0930-1120 Session 13 Invited Lectures (IL): Chair: T. Kundu
IL 17: Sobhan Sen, “Origin of Slow Solvation Dynamics in DNA: What is the
Biological Significance?”
IL 18: Bhargava Ram Nirghantam, “Ultrafast Photoelectron-Photoion
Coincidence Imaging Spectrometer to Explore Molecular Chirality”
IL 19: Mukesh Jewariya, “Real-Time Four-Dimensional Spatio-Temporal
Terahertz Imaging using Intense Terahertz Pulse”
1120-1150 Tea
1150-1240 Session 14: Plenary Lecture 6: Chair: D. K. Palit
S. Umapathy “Ultrafast Raman spectroscopy: Applications to chemical
dynamics”
1245-1315 Closing session
1315 Lunch
5
Table of Contents:
PLENARY
ABSTRACTS
November 7
PLENARY
TALK 1
Hirendra N.
Ghosh
Exciton, Bi-Exciton, Trion and Polaron Dissociation
Dynamics in Nano-Structured Hetero Interface:
Implication in Solar Devices
10
PLENARY
TALK 2 Keisuke Tominaga
Hydrogen-bond dynamics of 9-fluorenone derivatives
in water probed by 2D-IR spectroscopy 11
PLENARY
TALK 3 D. D. Sarma
Experiments in the sub-ps regime to understand
properties of opto-electronic materials 12
November 8
PLENARY
TALK 4 Shaul Mukamel
Nonlinear spectroscopy and imaging of molecules
with x-ray, quantum, and noisy light 13
PLENARY
TALK 5
G. Ravindra
Kumar
Ultrafast evolution of dense, hot plasmas Physics and
measurements in extreme conditions 14
PLENARY
TALK 6 S. Umapathy
Ultrafast Raman spectroscopy: Applications to
chemical dynamics 15
INVITED
LECTURES
ABSTRACTS
November 7
INVITED
LECTURE 1 Vandana Sharma
Transient negative polarizability frustrates
alignment in ultrashort laser induced fragmentation
of molecules
16
INVITED
LECTURE 2
Jyotishman
Dasgupta
Elucidating the Transient Raman Signature of a
Twisted Intramolecular Charge Transfer State 17
INVITED
LECTURE 3
Jean Christophe
Tremblay
How to use electronic flux density maps as a tool to
unravel ultrafast correlated electron dynamics 18
INVITED
LECTURE 4 Sayan Bagchi The curious case of warfarin photophysics 19
INVITED
LECTURE 5
Mahesh
Hariharan
Ultrafast Excited State Dynamics of Twisted
Aromatics 20
INVITED
LECTURE 6 Prasun K. Mandal
Effect of Alloy-Shelling on Ultrafast Dynamics in
Semiconductor Quantum Dots 21
6
INVITED
LECTURE 7 Anand Moorti
Electron Acceleration using Laser Fields at Extreme
Intensities in Plasmas: An Advanced Accelerator
Concept
22
INVITED
LECTURE 8 Kamal P. Singh 23
INVITED
LECTURE 9 Pankaj Mandal
Probing The Origin of Self Trapped Excitons in
Hybrid Lead Halide Perovskites Using Time-
Resolved Spectroscopy
24
INVITED
LECTURE 10
Sivarama
Krishnan
Opportunities in ultrafast science with laser
generated XUV pulses 25
November 8
INVITED
LECTURE 11 Anshu Pandey 26
INVITED
LECTURE 12
Rajesh K
Kushawaha
Photoionization of polyatomic molecules: Molecular
structure, ultrafast dynamics and molecular movie 27
INVITED
LECTURE 13 Parinda Vasa
Ultrafast dynamics in metal/semiconductor
nanostructures 28
INVITED
LECTURE 14 Adam Kirrander Ultrafast X-ray Scattering of Molecular Dynamics 29
INVITED
LECTURE 15 Dipanshu Bansal
Probing lattice instabilities in thermoelectric SnSe
using spectroscopic studies 30
INVITED
LECTURE 16 G. Naresh Patwari
Intermolecular Tuning of Non-Adiabatic dynamics
via Hydrogen Bonding 31
November 9
INVITED
LECTURE 17 Sobhan Sen
Origin of Slow Solvation Dynamics in DNA: What is
the Biological Significance? 32
INVITED
LECTURE 18 N Bhargava Ram
Ultrafast photoelectron-photoion coincidence
imaging spectrometer to explore molecular chirality 33
INVITED
LECTURE 19 Mukesh Jewariya
Real-Time Four-Dimensional Spatio-Temporal
Terahertz Imaging using Intense Terahertz Pulse 34
POSTER
ABSTRACTS
POSTER 1 Annyesha Biswas Stabilization and sensing of G-quadruplex DNA
structures with indolylquinolinium based probes 36
POSTER 2 Nibedita Pal Enzyme product releasing mechanism under
piconewton force manipulation: A single molecule 37
7
investigation using photon time-stamping
spectroscopy
POSTER 3 Partha Pyne Polyethylene glycols affect electron transfer rate in
phenosafranin-DNA 38
POSTER 4 Sk Imadul Islam Investigation on the ESPT Dynamics of D‑Luciferin
in Aqueous trifluoroethanol and ethanol Mixtures 39
POSTER 5 Arup Kundu Formation of Long Lived Triplets through Singlet
Fission in Lycopene Aggregates 40
POSTER 6 Sneha Paul Conformational Dynamics of c-MYC Promoter
based i-Motif DNA in Crowded Environments 41
POSTER 7 Tanuja Kistwal Solvation dynamics in solvent free protein – polymer
surfactant biomolecular assemblies 42
POSTER 8 Narayan Chandra
Matiy
Solute and Solvent Dynamics in Neat, and Wet-
Octanol: Steady State and Time Resolved
Fluorescence Measurements
43
POSTER 9 Rohit Goswami Ultrafast Control for Perfumery Industries 44
POSTER 10 Meghna Ghosh
Unveiling the Effect of Sugars on Dynamics of
Different Fluorophores in the Interior of Aerosol OT
Lamellar Structures: From Picosecond-to-
Femtosecond Study
45
POSTER 11 Harsh Bhatia
Use of Dimeric Excited States of the Donors in D4-A
Systems for Accessing White light Emission,
Afterglow and Invisible Security Ink
46
POSTER 12 Deepika Sardana Origin of Slow Solvation Dynamics in DNA: DAPI in
Dickerson-DNA 47
POSTER 13 Arnab Sil
Impact of Urea on Structure and Dynamics of an
Ionic Deep Eutectic Solvent: Exploration through
Reactive and Non-Reactive Solute Centered
Dynamics
49
POSTER 14 Pranav Adhyapak Solvation Dynamics in Mycobacterial Membranes
Probed by Time-Resolved Laurdan Fluorescence 50
POSTER 15 Sangita Kundu
Modulating Interaction Mechanism of Duplex DNA
with Graphene Oxide Employing Two Diverse
Binders
51
POSTER 16 Tanmay Goswami
Room Temperature Exciton and Trion Formation in
Monolayer MoS2 Followed by Dissociation in
Presence of Au NPs
52
POSTER 17 Fariyad Ali Ultrafast carrier dynamics of Cu doped CdSe
nanotetrapods 53
POSTER 18 Surya Narayan
Panda
Ultrafast all-optical detection of interfacial spin
transparency for pure spin current transport in
CoFeB/β-Ta thin films
54
POSTER 19 Apurba De
Synthesis and Carrier Dynamics of Highly
Luminescent Violet- and Blue-Emitting Perovskite
Nanocrystals
55
POSTER 20 Debashis Panda Facets of Carbon Nanodot: Fundamentals and
Applications 56
POSTER 21 Soumyadip
Bhunia
Ultrafast photoinduced electron transfer dynamics
between cyclometalated rhodium and iridium
complexes and cyan emitting copper nanoclusters
57
8
POSTER 22 T. Singha Determination of dispersion of the third order
optical nonlinearity of Carbon Dots 58
POSTER 23 Sayan Prodhan
Investigation of Improved Charge Carrier Dynamics
of Core-Shell Nanocrystal Modified Perovskite using
Transient Absorption Spectroscopy
59
POSTER 24 Sushanta Lenka
Study of Non-colinear Femtosecond Second
Harmonic and Sum Frequency Generation using
BBO crystals
61
POSTER 25 Hemen Gogoi Solvent Mediated Relaxation Dynamics of Core-Shell
Au-SiO2 Nanoparticles 62
POSTER 26 Bala Gopal M Ultrafast dynamics of gold dimers and trimers 63
POSTER 27 Gurpreet Kaur
Slow Charge Carrier cooling in Type-1 3D/0D Core-
Shell CsPbBr3@Cs4PbBr6 Perovskite system: Role
of Polaron Formation
64
POSTER 28 Jamuna K.
Vaishnav
Long-Range Resonance Coupling-Induced Surface
Energy Transfer from CdTe Quantum Dot to
Plasmonic Nanoparticle
65
POSTER 29 Binit Mallick
Time Dependent Optical Second Harmonic
Generation from Si/SiO2 Interface and Its Variation
with Doping Concentration
66
POSTER 30 Arundhati
Adhikari
Direct Observation of -Phonon Driven Ultrafast
Magnetization Dynamics in Ferromagnetic Nanodot
Arrays
67
POSTER 31 Kamlesh Kumar
Chauhan
Comprehensive study of femtosecond transient
carrier dynamics in mixed halide perovskite 68
POSTER 32 D. P. Khatua
Carrier Dynamics Measurement on MoS2
Monolayers Using Ultrafast Pump-Probe
Spectroscopy
69
POSTER 33 Manobina
Karmakar
Exploring the Dynamics of Excited Excitonic
Rydberg Series in Layered MoS2 70
POSTER 34 R. Rathore
Comparative study of ultra-fast thermal strain
evolution in Ge (111) sample induced by
fundamental and second harmonic pump pulse
71
POSTER 35 Sourav Sahoo Ultrafast Magnetization Dynamics in Ferromagnetic
Nanodot Arrays Connected by Nanochannels 72
POSTER 36 Nihit Saigal
CuFeS2 Quantum Dots based broadband (visible to
MIR) photodetector for detecting radiation from
ultrafast sources
73
POSTER 37 Koustuv Dutta Ultrafast Spin-Wave Dynamics in Ferromagnetic
Diamond Antidot Lattice 74
POSTER 38 Chayan Kumar De
Understanding Optical Behaviour of InP Based Core
Alloy Shell QDs through Ultrafast dynamics and
Single Particle Spectroscopy
75
POSTER 39 Asha Singh
Ultrafast Response of Nanoplatelets Around its
Particle Plasmon Resonance: Effect of Size
Distribution
76
POSTER 40 Amitabha Nandi
Singlet Fission within Ultrafast Time Scale and near
Unity Yield in 5,12–bis (phenylethynyl)tetracene thin
film
77
POSTER 41 Subhadip Roy
Cosolvents at Aqueous Interface: As Observed by
“Classical” and “Heterodyne-Detected” Vibrational
Sum Frequency Generation Spectroscopy: Subhadip
Roy
78
POSTER 42 Swetapuspa
Soumyashree
Cold Target Recoil Ion Momentum Spectroscopy:
Design and Simulation 79
9
POSTER 43 Madhusudhan P Study of molecular alignment using femtosecond
laser pulses 80
POSTER 44 Remya
Ramakrishnan
Anomalous Halogen–Halogen Interaction Assists
Radial Chromophoric Assembly 81
POSTER 45 Reshma Mathew
Excited state structural dynamics of 4-cyano-4’-
hydroxystilbene: deciphering the signatures of
proton-coupled electron transfer using ultrafast
Raman loss spectroscopy
82
POSTER 46 Srijan Chatterjee
Hydrocarbon Chain-Length Dependence of Solvation
Dynamics in Alcohol-based Deep Eutectic Solvents:
A 2D IR Spectroscopic Investigation
83
POSTER 47 Animesh Patra
Extremely Weakly Interacting O-H in the Hydration
Shell of High Charge Density Metal Ions as Observed
Raman Difference with Simultaneous Curve Fitting
(RD-SCF) Spectroscopy
84
POSTER 48 Atanu
Bhattacharya Attosecond (10-18 second) Charge Migration 86
POSTER 49 Kanika Jain
Energy Transfer followed by Sequential Electron
Transfer in a Supramolecular Tetrad Composed of
Phenothiazine, Zinc Porphyrin,
Borondipyyromethene, and Fullerene: Charge
Stabilization in “Antenna-Reaction Center” Mimic
87
POSTER 50 Lasitha P
Squaramide Based, “Turn-on” Schiff Base Multi-
analyte Sensors for Zn2+ and Cd2+: Influence of
Acetate ion and Co-operativity
88
POSTER 51 Sharmistha Das Dynamics of Preferential Solvation of 5-
Aminoquinoline in Hexane-Alcohol Solvent Mixtures 89
POSTER 52 Souradip
Dasgupta Excited State Dynamics of Fluorogenic Molecules 90
POSTER 53 C. Aparajit Efficient Generation of Ultrahigh-Contrast High-
Intensity Laser Pulses 91
POSTER 54 Habib Ali Enhanced Two-Photon Activity with Extended
Molecular Conjugation 92
POSTER 55 Kamalesh Jana
Femtosecond time resolved, micrometer space
resolved two dimensional velocity mapping of an
ultraintense laser driven solid plasma
93
POSTER 56 Pranav Bhardwaj Design and Development of a new High Harmonic
Generation (HHG) setup and XUV beamline 94
POSTER 57 Sunandita Paul Towards Light Induced Carbocation Generation in a
Supramolecular Cavity 95
POSTER 58 H. Singhal High order harmonic generation from noble gases
using annular laser beam 96
POSTER 59 Chinmoy Biswas
Femtosecond Transient Absorption Dynamics of π-
Extended Thioalkyl Substituted Tetrathiafulvalene
Sensitizers on TiO2 Thin Films
97
POSTER 60 Sukriti Santra Effect of charge state on the ultrafast dynamics of
molecular rotor 100
POSTER 61 Mrudul M S High-Harmonic generation from spin-polarised
defects in solids 101
POSTER 62 Sucharita Giri Probing molecular chirality via laser-induced
electronic fluxes 102
POSTER 63 Irafana N. Ansari
Characterizing Laguerre-Gaussian pulses using
Angle-resolved Attosecond
Streaking
103
POSTER 64 Sushil S. Sakpal The curious case of warfarin photophysics 104
POSTER 65 Ankur Mandal IR-IR control of High Harmonic Generation 105
10
POSTER 66 Arpita Mukherjee Temporal evolution of radiative rate reveals the
localization of holes in CuInS2-based quantum dots
PLENARY TALK 1:
Exciton, Bi-Exciton, Trion and Polaron Dissociation Dynamics in Nano-
Structured Hetero Interface: Implication in Solar Devices
Hirendra N. Ghosha, b
a Professor, Institute of Nano Science and Technology, Mohali, Punjab 160064 b Scientic Officer,, Bhabha Atomic Research Centre, Mumbai-400085, India
E-mail: hnghosh@inst.ac,in, hnghosh2004@gmail.com
Exciton and multi-exciton harvesting from semiconductor quantum dot is an
important phenomena to improve the photo-conversion efficiency in solar cell devices in
particular quantum dot sensitized solar cells (QDSC) and also photodetectors. Till date, not
many reports are available where relation between exciton/multi-exciton/trion dissociation
in semiconductor hetero-structure and boosting the power conversion efficiency (PCE) of
QDSC are discussed. Herein we report detailed ultrafast spectroscopic investigation on the
dissociation dynamics of exciton, bi-exciton and trion on metal-semiconductor hetero-
interface with the help of Femto-second broad-band pump-probe spectrometer. Ultrafast
transient absorption studies suggest that in metal-semiconductor hetero-interface exciton,
bi-exciton and trion dissociates very efficiently and as a proof-of-concept efficiency in
QDSC was found to increase by more than double. In addition to that ultrafast hot carrier
cooling is the key loss channel which limits achievable solar conversion efficiency.
Delaying the carrier cooling high efficient hot-carrier solar cell can be realized. Herein we
have demonstrated dramatic dip in the cooling rate in Type‑ 1 3D/0D CsPbBr3@Cs4PbBr6
core−shell NCs as compared to CsPbBr3 NCs in similar condition. Clear evidence of
polaron formation was observed in the core−shell system which was suppressed in the case
of CsPbBr3 NCs. The above findings can be efficient approaches towards the design and
development of efficient solar cell and optoelectronic devices using the principles of
multiexciton/trion generation and extracting them in metal-semiconductor nano-hybrid
system and slowing down the charge carriers through polaron formation in Type-1 core-
shell system.
REFERENCES:
1. T. Goswami, R. Rani, K. S. Hazra, and H. N. Ghosh*
J. Phys. Chem. Lett, 2019, 10, 3057.
11
2. G. Kaur, K. J. Babu, N. Ghorai, T. Goswami, S. Maiti, and H. N. Ghosh*
J. Phys. Chem. Lett, 2019, 10, 5302.
3. T. Debnath and H. N. Ghosh*J. Phys. Chem. Lett, (Perspective) 2019, 10,
(Accepted)
PLENARY TALK 2:
Hydrogen-bond dynamics of 9-fluorenone derivatives in water probed
by 2D-IR spectroscopy Masaki Okuda, Kaoru Ohta, Keisuke Tominaga
Molecular Photoscience Research Center, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe, Hyogo 657-
8501, Japan .
In aqueous solution, hydrogen bond (HB) between solute and solvent molecules
strongly perturbs dynamic and static properties of the solute molecules, which affects the
reactivity of chemical reaction in solution. Vibrational frequency is well-known to be
sensitive to the environmental change around solute molecules in solution. Two-
dimensional infrared (2DIR) spectroscopy is a powerful tool to quantify the vibrational
frequency fluctuation of solute molecules, which results from the temporal fluctuation in
solute-solvent interaction on an ultrafast time scale (sub-ps ~ ps time scale).
In this study, by using 2DIR spectroscopy, we have investigated the vibrational
frequency fluctuations of two different 9-fluorenone derivatives (FL-2COO− and FL-
4COO−) in D2O. From the center line slope analyses for their 2D-IR spectra, we found that
the frequency-frequency time correlation function (FFTCF) of the CO stretching mode of
FL-4COO− has a decay time constant of 2.7 ps, which is much longer than those of ionic
vibrational probe molecules (~1 ps) observed in many studies so far. The decay time of
FFTCFs of the related compounds shows a strong correlation with the size of the
hydrocarbon part, which is hydrophobic in nature; acetaldehyde, the smallest size molecule
has a time constant of 1.4 ps. Consequently, our 2D-IR results clearly demonstrate that the
size of the hydrocarbon part plays an important role in the vibrational frequency
fluctuations in water. To understand the effect of the hydrocarbon part on local
environment at a molecular level, we conducted the theoretical analyses with classical
molecular dynamics (MD) simulations for the FL-4COO−/water system. We found that the
hydrogen bond dynamics between solute and water and the reorientational relaxation of a
single water molecule in the vicinity of solute are similar to those in the bulk, which
suggests that the slow decay of the FFTCF is not solely due to single-molecule dynamics
around the solute. By calculating the radial dependence of the Coulomb electrostatic
potential on the vibrational probe from water molecules, we found that the solute interacts
electrostatically with water molecules in a sphere of a radius 8 Å from the solute. From this
result, we conclude that collective water dynamics, which is intrinsically slower than the
single-molecule dynamics, makes a strong impact on the vibrational frequency fluctuations
of FL-4COO− in water.
On the other hand, the IR spectrum of FL-2COO− in D2O exhibits the asymmetric
lineshape, which likely results from two different types of solute-water HB complexes. We
found that the relative amplitude of the cross peak (SAB) to the diagonal peak signals (SAA)
becomes larger with population time T, which reflects the making and breaking of a HB
12
between FL-2COO− and a water molecule. Based on these 2DIR results, we conclude that
the position of the COO− group plays an important role for the solute-water HB dynamics.
PLENARY TALK 3:
Experiments in the sub-ps regime to understand properties of opto-
electronic materials
D. D. Sarma Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012,
sarma@iisc.ac.in
Self-absorption has been a major impediment to utilizing brilliant and tunable
photoluminescence from semiconductor nanocrystals, as it reduces drastically the quantum
efficiency at any reasonable optical density. In this context, defect emissions are interesting
because of their Stokes shifts that make them impervious to self-absorption, but this comes
often at the cost of the quantum efficiency and the tunability. We have been addressing
these issues for many years and have overcome these challenges in carefully designed
systems.1-4 Ultrafast spectroscopic studies allow us to probe the origin of the high quantum
efficiencies in such systems and I shall discuss two such systems in this talk.
If time permits, I shall also discuss a fundamental issue related to the spectacular
photovoltaic properties observed in hybrid perovskite halides and address the intriguing
possibility of an excited state polarization of the material due to the presence of dynamical
dipoles in the ground state.5
These three examples illustrate different time-resolved techniques that we employ
to understand properties of materials within our group.
REFERENCES:
1. Abhijit Hazarika et al., Phys. Rev. Lett. 2013, 110, 267401.
2. Abhijit Hazarika, Anshu Pandey, and D. D. Sarma, J. Phys. Chem. Lett. 2014, 5, 2208.
3. Abhijit Hazarika et al., unpublished results
4. Shyamashis Das et al., unpublished results.
5. Sharada Govinda et al., J. Phys. Chem. Lett. 2017, 8, 4113.
13
PLENARY TALK 4:
Nonlinear spectroscopy and imaging of molecules with x-ray, quantum,
and noisy light Shaul Mukamel
Department of Chemistry and Department of Physics and Astronomy, University of California, Irvine,
Irvine, California 92697-2025, USA
s.mukamel@uci.edu
Ultrafast nonlinear x-ray spectroscopy is made possible by newly developed free
electron laser and high harmonic generation sources. The attosecond duration of X-ray pulses
and the atomic selectivity of core X-ray excitations offer a unique combination that can monitor
elementary molecular events with high spatial and temporal resolution. Applications of these
techniques to spectroscopy and imaging of molecules will be presented. X ray sum frequency
generation, circular dichroism and time- and frequency-resolved ultrafast diffraction of noisy
X-ray pulses will be discussed.
Quantum light opens up new avenues for spectroscopy by utilizing parameters of the
quantum state of light as control knobs and through the variation of photon statistics by
coupling to matter. When a molecule interacts with an external field, the phase information is
imprinted in the state of the field in a detectable way. Nonlinear optical signals induced by
quantized light fields and entangled photon pairs will be discussed. Combined time and
frequency resolution not possible by classical light can be achieved. A novel quantum
diffraction-based imaging technique whereby one photon of an entangled pair is diffracted of
a sample and detected in coincidence with its twin is presented. Imaging with weak quantum
fields is possible, avoiding damage to delicate biological samples.
REFERENCES: [1] Jérémy R. Rouxel, Markus Kowalewski, Kochise Bennett, Shaul Mukamel. Phys. Rev. Lett. 2018,120,
243902
[2] Frank Schlawin, Konstantin E. Dorfman and Shaul Mukamel. Acc. Chem. Res., 2018,51, 2207-2214
[3] Shahaf Asban, Konstantin E. Dorfman, and, Shaul Mukamel. PNAS. 2019, 116, 11673-11678
[4] Shahaf Asban, Daeheum Cho, and Shaul Mukamel. J.Phys.Chem.Lett, 2019, 10, 5805-5814
14
PLENARY TALK 5:
Ultrafast evolution of dense, hot plasmas
Physics and measurements in extreme conditions
G. Ravindra Kumar Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005.
(grk@tifr.res.in; www.tifr.res.in/~uphill)
High intensity, ultrashort light pulses (>1018 W cm-2, femtosecond duration) create
unusually hot and dense plasmas, enabling laboratory simulation of astrophysical
phenomena, relativistic optics, particle acceleration on a table top, real time x-ray
diffraction of the condensed phase, biological imaging or medical therapies for cancer1.
Visible/infrared laser light (~eV photon energy) can create relativistic (> MeV) electrons
in a target via collective plasma processes. Much of the subsequent physics and resulting
applications demand a good understanding of the generation and transport of these
electrons. A big challenge is to capture the experimental signature of a particular
phenomenon, given the highly noisy, turbulent and rapidly changing environment in the
plasma.
This talk will illustrate several aspects of the ultrafast evolution of relativistic
electron beam transport in a solid2, its energy dissipation3, megagauss magnetic fields4
that these electrons generate, extremely strong shocks5-7 caused by the laser pulse etc,- all
using pump-probe methods. Similarities between our results and astrophysical
observations indicate exciting possibilities that table top terawatt lasers offer for
laboratory astrophysics8.
REFERENCES:
1. S.V. Bulanov et al., Plasma Physics Reports, 2015, 41, 1
2. G. Chatterjee et al., Phys. Rev. Lett. 2012, 108, 235005
3. M. Shaikh et al., Phys. Rev. Lett. 2018,120, 065001
4. S. Mondal et al., Proc. Natl. Acad. Sci. (USA) 2012, 109, 8011
5. S. Mondal et al., Phys. Rev. Lett. 2010, 105, 105002
6. A. Adak et al., Phys. Rev.Lett. 2015, 114, 115001
7. K. Jana et al., 2019 (in preparation)
8. G. Chatterjee et al., Nat. Commun. 2017, 8, 15970
15
PLENARY TALK 6:
Ultrafast Raman spectroscopy: Applications to chemical dynamics S Umapathy 1,2
1 Dept. of Inorganic and Physical Chemistry 2Department of Applied Physics and Instrumentation, Indian Institute of Science, India.
Nonlinear spectroscopy [1] (NL) uses multiple (n) laser fields to extract the molecular
properties. Several nonlinear spectroscopic techniques have been introduced to provide
better understanding of the molecular properties. Nonlinear Raman spectroscopy
(NLR) is one such nonlinear process where the Raman pump and the Raman probe
beams drive the Raman transition in the system. Nonlinear Raman spectroscopy is very
promising and is very useful in understanding the structural and dynamical information
of a complex polyatomic molecular system. Femtosecond stimulated Raman
spectroscopy (FSRS) [2-3] is a NLR process wherein Raman pump (picosecond pulse)
and Raman probe, a white light continuum (femtosecond pulse) drive the Raman
transition and is a promising technique to understand the structural and dynamical
information of molecular systems. It provides good spectral (~15cm-1) and temporal
resolution (~50fs).
Ultrafast Raman loss spectroscopy (URLS), [4-10] also a NLR process of third order
developed by our group is more sensitive than FSRS. URLS provides twice the
intensity of FSRS signals and doesn’t interfere with fluorescence background on
resonance excitation which is usually a big hurdle in spontaneous Raman
measurements and sometimes in FSRS. URLS has been applied to get the Raman
spectra of several systems ranging from non-fluorescent to fluorescent systems. The
interaction of the solute with the surrounding molecules, usually solvent molecules
influences the Raman frequency and its linewidths. The dephasing times of vibrational
modes range from subpicosecond to picoseconds which depend on the kind of
interaction and molecular system. URLS has been applied to understand and measure
the dephasing process in vibrational modes both in the electronic ground and excited
molecular states. The response of the Raman line shapes on resonance excitations [8-
9] has been studied using URLS. The femtosecond time resolved Raman spectra of t-
stilbene and other systems will be discussed.
References
[1]. F. Ariese, K. Roy, V. Ravi Kumar, H. C. Sudeeksha, S. Kayal, and S. Umapathy, John Wiley and Sons,
DOI: 10.1002/97804- 70027318.a9555, (2017).
[2]. K. Roy, S. Kayal, N. K. Rai, and V. Ravikumar, Chapter: Editors: J. A. K. Howard, H. A. Sparkes, P. R.
Raithby, A.V. Churakov, Springer pp. 25-42, (2014).
[3]. B. Mallick, A. Lakshmanna, V. Radhalakshmi, S. Umapathy Curr. Sci. 95, 1551 (2008).
[4]. S. Umapathy, A. Lakshmanna, B. Mallick J. Raman Spectrosc. 40, 235 (2009).
[5]. A. Lakshmanna, B. Mallick, S. Umapathy Curr. Sci. 97, 210 (2009).
[6]. B. Mallick, A. Lakshmanna, S. Umapathy J. Raman Spectrosc. 42, 1883 (2011).
[7]. N. K. Rai, A. Lakshmanna, V. Namboodary, S. Umapathy J. Chem. Sci. (2011).
[8]. S. Umapathy, B. Mallick, A. Lakshmanna J. Chem. Phys. 133, 024505 (2010).
[9] K. Roy, S. Kayal, V. Ravi Kumar, F. Ariese, A. Beeby, S. Umapathy. J. Phys. Chem. A 35, 6538 (2017).
[10] K. Roy, S. Kayal, F. Ariese, A. Beeby and S. Umapathy. J. Chem. Phys. 146, 064303 (2017).
16
INVITED LECTURES: IL 1
Transient negative polarizability frustrates alignment in ultrashort
laser induced fragmentation of molecules
Arnab Sen1, T. Sairam2, B. Bapat1, R. Gopal2*,V. Sharma3*
1 Indian Institute of Science Education and Research, Pune, Maharashtra, 411008, India 2 Tata Institute of Fundamental Research, Hyderabad, 500107, India
3 Indian Institute of Technology, Hyderabad, 502285, India
*email address: ramgopal@tifrh.res.in, vsharma@iith.ac.in
Polarizability is a fundamental molecular property governing inter-molecular and
light-molecule interactions. Molecules, seeking to minimize their energy in the presence
of a short lived but intense laser field, undergo rotation and alignment mediated through
the static polarizability. Here, we demonstrate an anomalous suspension of this alignment,
as observed through the velocity imaging of the fragmentation following the strong field
ionization of O2 molecule by ultrashort (35 fs, 400 nm) laser pulses. Alternately, in
concomitant experiments with 800 nm laser pulses (25 fs), the expected alignment is indeed
observable. We analyze these results in conjunction with a semi-classical model of the
induced rotation in the molecular ion involving polarizabilities of the participating excited
states. It emerges that a transient negative polarizability on the time scales of several
femtoseconds frustrates the alignment of the molecular ion. This singular molecular
behaviour, visualized here for the first time in fragmentation, is not only of fundamental
interest, but can potentially be applied for terahertz photonics.
17
INVITED LECTURES: IL 2
Elucidating the Transient Raman Signature of a Twisted
Intramolecular Charge Transfer State Jyotishman Dasguptaa
a Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai.
Charge transfer (CT) states provide a facile access to separate strongly bound
excitons (electron-hole pairs) in organic materials thereby enabling robust initiation of
photochemistry. From photocatalytic fuel synthesis to functional materials for photovoltaic
devices, the efficiencies of all the light-triggered processes critically depend on tuning the
energy, spatial extent and lifetime of the CT states. In this talk, I will describe our efforts
to visualize the ‘twisted intramolecular charge transfer’ (TICT) state in biomolecular
fluorescent probes that show large structural relaxation in the excited state. We find an
unequivocal transient Raman signature of the TICT state in mitochondrial staining donor-
π-acceptor class of stillbazolium dyes. Resonance-enhanced femtosecond stimulated
Raman spectroscopy (FSRS)1 of 4 N,N-diethylamino-4˝-Nˊ-methyl-stilbazolium tosylate
(DEST) revealed the appearance of a distinct blue-shifted vibrational peak at 1650 cm-1.2
Using electronic structure calculations with explicit solvent models, the peak was assigned
to a new mode: an isolated pyridinium ring symmetric C=C stretch belonging to the TICT
excited state of DEST. The rise and decay of the TICT 1650 cm-1 Raman marker mode
captured by FSRS correlates with the excited state dynamics obtained via femtosecond
broadband transient absorption (TA) spectroscopy. Our study demonstrates that time-
resolved vibrational Raman spectra, interpreted with support from appropriate electronic
structure calculations can be an effective structural probe for identifying the spatial location
of the “twist” in TICT-based molecular dyes.
REFERENCES:
1. Palas Roy,
2. Shreetama Karmakar, to be submitted.
18
INVITED LECTURES: IL 3
How to use electronic flux density maps as a tool to unravel ultrafast
correlated electron dynamics Jean Christophe Tremblaya
a Laboratoire de Physique et Chimie Théoriques CNRS/Université de Lorraine - UMR 7019, 1 Bd Arago,
57070 Metz (France) jean-christophe.tremblay@univ-lorraine.fr
Understanding how electrons flow during reactions remains a question of central
importance in chemistry, as it helps unravelling the mechanism of electron rearrangements
leading to chemical transformations and to the emergence of specific properties. In this
contribution, I illustrate how time-dependent electronic current density maps can be used
to visualize and interpret such processes from first principles many-electron dynamics
simulations. These quantities are related by the quantum continuity equation, which is a
reformulation of the many-body Schro ̈dinger equation into a one-body hydrodynamic-like
transport equation.
I will first introduce a many-body wave-function simulation method, the Time-
Dependent Determinantal Configuration Interaction (TD-detCI), to study light-induced
ultrafast charge migration dynamics in rigid molecules and nanostructures. A posteriori
reduction of the many-body electronic wave packets dynamics then leads to the electronic
continuity equation, which allows to follow the time-evolution of electrons as the flow of
an electronic fluid. I will further show how time-resolved X-ray diffraction measurements
are related the transient electronic flux density.
To investigate chemical reactions, I will explain how an electronic continuity
equation can be derived within the Born-Oppenheimer approximation, and how the
associated current density can be used to extract mechanistic information about electron
reorganization during simple reactions. This new visualization technique provides an
unbiased first principles approach for drawing curly arrows – a concept dear to the chemists
when rationalizing reaction mechanisms.
REFERENCES:
1. G. Hermann, V. Pohl, and J.C. Tremblay “An Open-Source Framework for Analyzing N-Electron
Dynamics: II. Hybrid Density Functional Theory/Configuration Interaction Methodology”, J.
Comput. Chem. 38, 2378 (2017).
2. G. Hermann, V. Pohl, G. Dixit, and J.C. Tremblay “Probing Electronic Fluxes via Time-Resolved
X-ray Scattering”, arXiv:1907.00891 (2019).
3. V. Pohl and J.C.Tremblay “Adiabatic Electronic Flux Density: A Born-Oppenheimer Broken
Symmetry Ansatz”, Phys. Rev. A 93, 012504 (2016).
19
INVITED LECTURES: IL 4
Hydrocarbon Chain-Length Dependence of Solvation Dynamics in Alcohol-Based
Deep Eutectic Solvents: A 2D IR Spectroscopic Investigation
Sayan Bagchi, Srijan Chatterjee, Deborin Ghosh, Tapas Haldar, Pranab Deb, Sushil S.
Sakpal, Samadhan H. Deshmukh, Somnath M. Kashid
Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, Pune 411008, India
Deep eutectic solvent (DES) has gained popularity in recent years as an
environmentally benign, inexpensive alternative to organic solvents for diverse
applications in chemistry and biology. Among them, alcohol-based DESs serve as useful
media in various applications due to their significantly low viscosity as compared to other
DESs. Despite their importance as media, little is known how their solvation dynamics
change as a function of the hydrocarbon chain-length of the alcohol constituent. In order
to obtain insights into the chain-length dependence of the solvation dynamics, we have
performed two-dimensional infrared spectroscopy on three alcohol-based DESs by
systematically varying the hydrocarbon chain-length. The results reveal that the solvent
dynamics slow down monotonically with increase in the chain-length. This increase in the
dynamic timescales also show a strong correlation with the concomitant increase in the
viscosity of DESs. In addition, we have performed MD simulations to compare with the
experimental results, thereby testing the capacity of simulations to determine the
amplitudes and timescales of the structural fluctuations on fast timescales under thermal
equilibrium conditions
REFERENCES
1. J. Phys. Chem B, DOI: 10.1021/acs.jpcb.9b08954
20
INVITED LECTURES: IL 5
Ultrafast Excited State Dynamics of Twisted Aromatics
Mahesh Hariharana
a School of Chemistry, IISER Thiruvananthapuram, mahesh@iisertvm.ac.in
Self-assembling of organic chromophoric systems into elegant supramolecular
architectures with emergent properties has received prodigious attention in recent years.1
The notion of ‘emergence upon assembly’ is evidenced in the unusual photoexcited state
dynamics exhibited by chromophoric assemblies. In the first example, a naphthalene-
naphthalimide donor-acceptor (D-A) dyad assembled into segregated D-A stacks in the
crystalline state (Figure 1). The photo-induced charge separated state in the aggregate state
lasts 10,000 times longer than the monomeric dyad. The femtosecond transient absorption
spectra depicted the spectroscopic signature for naphthalene dimer radical cation indicating
the migration of charges through the stacks.2 In the second example, we report the
crystalline evidence for Greek cross‐dipole (α=90°) stacking of 1,7‐dibromoperylene‐3,4,9,10‐tetracarboxylic tetrabutylester (PTE‐Br2) displaying null excitonic coupling and
thereby monomeric optical behavior. Additionally, the semi‐classical Marcus theory of
charge‐transfer rates predicted a selective hole transport phenomenon in the orthogonally
stacked PTE‐Br2.3 In the third example, we showcase a radial assembly of 1,8-
dibromonaphthalene(2,6-diisopropylphenyl)imide (NIBr2) in crystalline phase driven by
hexabromine synthon.4 NIBr2 exhibits ultrafast intersystem crossing5 and solid-state room
temperature phosphorescence. We believe the fundamental understanding of noncovalent
interactions dictating the unorthodox assembly of chromophores6 and probing of emergent
properties are paramount for the rational design and construction of robust functional
materials.
Figure 1. Representative strategies adopted in our group to spatially organize organic
chromophores for emergent properties.
REFERENCES
1. R. T. Cheriya, A. R. Mallia, M. Hariharan, Energy Environ. Sci. 2014, 7, 1661.
2. A. R. Mallia, P. S. Salini, M. Hariharan, J. Am. Chem. Soc. 2015, 137, 50, 15604.
3. E. Sebastian, A. M. Philip, A. Benny, M. Hariharan, Angew. Chem., Int. Ed. 2018, 57, 15696.
4. M. A. Niyas, R. Ramakrishnan, V. Vijay, E. Sebastian, M. Hariharan, J. Am. Chem. Soc. 2019, 141, 4536.
5. K. Nagarajan, A. R. Mallia, K. Muraleedharan, M. Hariharan, Chem. Sci. 2017, 8, 1776.
6. R. Ramakrishnan, M. A. Niyas, M. P. Lijina, M. Hariharan, Acc. Chem. Res. 2019, 52, ASAP
21
INVITED LECTURES: IL 6
Effect of Alloy-Shelling on Ultrafast Dynamics in Semiconductor Quantum Dots
Prasun K. Mandala,b aDepartment of Chemical Sciences, bCentre for Advanced Functional Materials, Indian Institute of Science
Education and Research (IISER) Kolkata, Mohanpur, West Bengal, 741246, India.
e-mail:prasunchem@iiserkol.ac.in
Ultra-bright and ultra-stable semiconductor quantum dots (QDs) are becoming
popular towards different applications such as LEDs, photovoltaics, optoelectronics, bio-
imaging etc.1-3 Different kinds of chemical modification towards obtaining optically
superior QDs will be discussed.4-10 QDs tend to follow Kasha's rule (i.e. excitation
wavelength independent PL emission maximum) but not the Vavilov's rule (i.e. excitation
wavelength independent PL quantum yield). Ultrafast dynamical investigations have been
employed to reveal details of exciton (both electron and hole) dynamics and also the effect
of interaction of the excitons with trap states towards modifications of the exciton
dynamics.7 Results obtained from these detailed analyses could explain why QDs follow
Kasha's rule but not Vavilov's rule.
Results from different types of core/alloy-shell QDs will be elaborated.
REFERENCES
1. J. S. Yao, J. Ge, B. N. Han, K. H. Wang, H. B. Yao, H. L. Yu, J. H. Li, B. S. Zhu, J. Z. Song, C.
Chen, Q. Zhang, H. B. Zeng, Y. Luo, S. H. Yu, J. Am. Chem. Soc. 2018, 140, 3626.
2. Q. A. Akkerman, M. Gandini, F. Di Stasio, P. Rastogi, F. Palazon, G. Bertoni, J. M. Ball, M. Prato,
A. Petrozza, L. Manna, Nat. Energy 2016, 2, 16194.
3. H. Zhang, X. Wang, Q. Liao, Z. Xu, H. Li, L. Zheng, H. Fu, Adv. Funct. Mater. 2017, 27, 1604382.
4. D. Hahm, J. H. Chang, B. G. Jeong, P. Park, J. Kim, S. Lee, J. Choi, W. D Kim, S. Rhee, J. Lim, et
al. Chem. Mater. 2019, 31, 3476-3484.
5. X. Shen, Y. Zhang, S. V. Kershaw, T. Li, C. Wang, X. Zhang, W. Wang, D. Li, Y. Wang, M. Lu,
L. Zhang, C. Sun, D. Zhao, G. Qin, X. Bai, W. W. Yu, A. L. Rogach, Nano Lett. 2019, 19, 1552-
1559.
6. D. Roy, T. Routh, A. V. Asaithambi, S. Mandal, P. K. Mandal, J. Phys. Chem. C 2016, 120, 3483-
3491.
7. D. Roy, A. Das, C. K. De, S. Mandal, P. R. Bangal, P. K. Mandal, J. Phys. Chem. C, 2019, 123,
6922-6933.
8. D. Roy, S. Mandal, C. K. De, K. Kumar, P. K. Mandal, Phys. Chem. Chem. Phys. 2018, 20, 10332-
10344.
9. C. K. De, T. Routh, D. Roy, S. Mandal, P. K. Mandal, J. Phys. Chem. C 2018, 122, 964-973.
10. C. K. De, D. Roy, S. Mandal and P. K. Mandal, J. Phys. Chem. Lett. 2019, 10, 4330-4338.
22
INVITED LECTURES: IL 7
Electron Acceleration using Laser Fields at Extreme Intensities in
Plasmas: An Advanced Accelerator Concept
Anand Moortia,b
a Advanced Plasma Acceleration Section, Laser Plasma Division, RRCAT, Indore 452013 b Faculty of Physics, Homi Bhabha National Institute, Anushakti Nagar, Mumbai 400094
E-mail: moorti@rrcat.gov.in
LASER is one of the greatest inventions in the modern time, and along with variety
of direct applications in almost every aspect of life, has also been recognized as a
ubiquitous tool for the progress of advanced science and technology. It could be possible
due to development of variety of lasers covering a wide range of parameters during last
several decades. In case of pulsed lasers, with successive advancements in the mode-
locking techniques, pulse duration has eventually been brought down in the femtosecond
(ultra-short) regime. Subsequently, using Chirped Pulse Amplification (CPA) technique,
ultra-short pulse duration laser systems providing peak powers of several Terawatt (TW)
to few Petawatt (PW) level became a reality. In CPA technique, an ultra-short duration
laser pulse is first temporally stretched, and after desired level of amplification in the
various amplifier stages, is compressed back to the ultra-short duration providing high peak
power. Impact of this technique on utilization of ultra-short pulse duration lasers in variety
of fields was widely appreciated when inventors of this scheme, G. Mourou and D.
Strickland, were jointly awarded Nobel Prize in Physics, 2018.
Availability of high-power ultra-short duration laser systems, providing extreme
intensities (~1018 Wcm-2 to greater than 1020 Wcm-2) when focused to a tiny spot of several
microns diameter, has dramatically changed the physics and applications of high-intensity
laser matter interaction1. One of the areas where it could have a profound impact is the
development of particle accelerators. Various advanced accelerator concepts on utilization
of huge electric fields associated with intense, ultra-short laser pulses have been proposed
and being investigated. Potential techniques based on laser plasma interaction at ultra-high
intensities, and utilization of laser as well as fields generated in plasma has been
developed2. For example, intense, ultra-short laser pulse could drive giant electron plasma
wave which could be used for accelerating electrons to few GeV in a small interaction
length of few cm. Such compact accelerators could also facilitate development of laser
driven synchrotron (x-rays and -rays) sources. In this talk, a brief overview of laser plasma
based advanced acceleration techniques, and recent experimental investigations performed
in this area at RRCAT, Indore, would be presented.
REFERENCES:
1. A. Moorti, Kiran: A Bulletin of the Indian Laser Association, 2015, 26(2), 19.
2. A. Moorti, Physics News, Bulletin of the Indian Physics Association, 2018, 48(3), 19.
23
Invited Lectures: IL 8
Kamal P. Singh
24
INVITED LECTURES: IL 9
PROBING THE ORIGIN OF SELF TRAPPED EXCITONS IN HYBRID LEAD
HALIDE PEROVSKITES USING TIME-RESOLVED SPECTROSCOPY
Shabnum M. Bhat, Sneha Banerjee and Pankaj Mandal Department of Chemistry, Indian Institute of Science Education and Research, Pune 411008, Maharashtra
India
Lead halide perovskites have emerged as an interesting class of materials
because of their marvelous photo-physical properties like high PL quantum yield, narrow
emission bandwidth, low threshold lasing, high PCE, etc.1 These unique properties are due
to their intrinsic defect tolerant band structure as compared to conventional
semiconductors. Lead halide perovskites crystalize in a variety of structures ranging from
3D to 0D. Lower dimensional lead halide perovskites (2D, 1D, 0D) show some interesting
optoelectronic properties. Interestingly, the optical properties in lower-dimensional lead
halide perovskites strongly depend upon A-site cation, which is not the case in 3D analogs.
In addition to quantum confinement, the lower dimensional perovskites also show
dielectric confinement.
We synthesized strongly confined one dimensional (1D) Pyridinium lead
bromide (PyPbBr3) perovskite single crystals. Due to strong confinement in two
dimensions and the presence of an aromatic cation, these perovskite crystals show
interesting optical properties. A strong and highly stokes shifted PL emission is observed,
at room temperature. The origin of this emission is attributed to exciton self-trapping.2 We
used Optically Heterodyned-Optical Kerr Effect Spectroscopy (OH-OKE) to understand
the mechanistic origin of this self-trapped excitonic emission and the role of aromatic π-
electron cloud in exciton self-trapping. Indeed there is a strong influence of presence of
this cation, which manifests in its optical properties and structural dimensionality.
REFERENCES:
[1] Akkerman Q., et.al, Nat. Mater., (2018), 394, 17.
[2] Smith D., et.al, Acc. Chem. Res., (2018), 619, 51.
25
INVITED LECTURES: IL 10
Opportunities in ultrafast science with laser generated XUV pulses Sivarama Krishnan
1 Department of Physics, Indian Institute of Technology – Madras, Chennai 600036, India.
Email:srkrishnan@iitm.ac.in
In this talk we will present some perspectives of intense laser matter interaction
leading to the generation of XUV pulses from commonly available NIR femtosecond
pulses and possible opportunities in using these to explore nanoscale matter based on
currently ongoing studies using synchrotron light. An analysis of the Strengths,
Weaknesses, Opportunities and Threats (SWOT) in this approach in comparison with
synchrotron and fast evolving free-electron laser pulses will be attempted. Bringing up
issues of coherence, mono- vs. poly-chromaticity, tenability, brilliance and related issues,
this talk intends to initiate and provoke discussion at this meeting, which will possibly be
both stimulating and spontaneous.
REFERENCES:
1. Krishnan, SR; Gopal, R; Rajeev, R; Jha, J; Sharma, V; Mudrich, M; Moshammer, R; Krishnamurthy,
M; Photoionization of clusters in intense few-cycle near infrared femtosecond pulses Physical Chemistry
Chemical Physics 16, 19, 8721-8730 (2014).
2.Buchta, Dominic; Krishnan, S. R et al., Charge transfer and penning ionization of dopants in or on
helium nanodroplets exposed to EUV radiation, The Journal of Physical Chemistry A 117, 21, 4394-
4403 (2013).
26
INVITED LECTURES: IL 11
Ansu Pandey
27
INVITED LECTURES: IL 12
Photoionization of polyatomic molecules: Molecular structure, ultrafast
dynamics and molecular movie
Rajesh K Kushawaha
AMOPH division, Physical Research Laboratory, Ahmedabad, 380009
Molecular rotations and vibrations are in picosecond to femtosecond time scale and
electron dynamics within atoms or molecules is in atto second time scale. Chasing and
controlling these dynamics will open an opportunity to do molecular engineering. The
femtosecond time resolved electron and ion imaging has been converted to movies for
understanding the structure and dynamics of molecular systems. In this talk, I will discuss
about photo induced processes in polyatomic molecules1. The molecular alignment using
pump-probe scheme and Velocity Map Imaging spectrometer will also be discussed. Recent
studies on the temporal evolution of electronic and nuclear wave packets created in strong-
field excitation of the carbon dioxide molecule using momentum-resolved ion spectroscopy
and channel-selective Fourier analysis will be presented. We found signatures of both,
electronic and vibrational excitations, which involve the ground and the first excited
electronic states, depending on the particular final state of the fragmentation2. Finally,
molecular movies on molecular rotation will be shown and related fundamental science will
be discussed.
REFERENCES: 1. Rajesh Kumar Kushawaha et al., Phys. Chem. Chem. Phys., 2019, 21, 13600-13610
2. Artem Rudenko et al, Faraday Discuss., 2016 194, 463-478
.
28
INVITED LECTURES: IL 13
Ultrafast dynamics in metal/semiconductor nanostructures Parinda Vasa
Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
In this talk we shall discuss ultrafast pump-probe experiments performed in the
visible range on metal and metal/semiconductor nanostructures [1,2]. The experiments
performed on gold thin films show transient reflectivity changes in the visible, which
are related to the electron distribution around Fermi energy. In case of metal-
semiconductor hybrid nanostructures, the transient absorption exhibit the manifestation
of Purcell effect or the polariton formation depending on the strength of light-matter
interaction energy. A significant reduction in the relaxation time of the emitters is
observed in the strong coupling regime [1, 2].
REFERENCES:
1. P. Vasa and C. Lienau, ACS Photonics 2018, 5, 2.
2. A. Singh, G. Sharma, B. P. Singh, and P. Vasa, J. Phys. Chem. C 2019, 123, 16965.
29
INVITED LECTURES: IL 14
Ultrafast X-ray Scattering of Molecular Dynamics Adam Kirrandera
a University of Edinburgh, School of Chemistry, Edinburgh, EH9 3FJ, UK, Adam.Kirrander@ed.ac.uk
Rapid developments of new x-ray and electron scattering experiments provide
exciting opportunities for the study of ultrafast photochemical and photophysical
processes1–4. The focus of this talk is on the intersection of theory, simulations, and
experiments5–7. In particular, we will discuss new types of experiments that might
transgress the distinction between structural dynamics and spectroscopy7. Using
comprehensive simulations of nonresonant ultrafast x-ray scattering from a molecular
wavepacket, we examine the components that contribute to the total scattering signal. The
simulations demonstrate how the elastic component, which can be used to determine the
spatio-temporal structural dynamics of the molecule, also carries an imprint of the
electronic structure, and how the inelastic component depends on the geometry of the
molecule. Most interestingly, mixed coherent contributions to the scattering directly probe
transient electronic coherences in the molecule.
Figure 1. An XUV pump pulse excites a wave packet from the ground state of H2 onto an excited state. After
excitation, an x-ray pulse probes the system by nonresonant ultrafast scattering7.
REFERENCES:
1. M. P. Minitti et al., Phys. Rev. Lett. 2015, 114 255501.
2. H.-W. Yong et al., J. Phys. Chem. Lett. 2018, 9, 6556.
3. B. Stankus et al., Nature Chem. 2019, 11, 716.
4. J. M. Ruddock et al., Science Adv. 2019, 5, eaax6625.
5. A. Kirrander et al., J. Chem. Theory Comput. 2016, 12, 957.
6. A. Kirrander, P. M. Weber, Applied Science 2017, 7, 534.
7. M. Simmermacher et al., Phys. Rev. Lett. 2019, 122 073003.
30
INVITED LECTURES: IL 15
Probing lattice instabilities in thermoelectric SnSe using spectroscopic
studies Dipanshu Bansala
a Department of Mechanical Engineering, IIT Bombay, Mumbai, MH 400076 Understanding of lattice instabilities is critical to rationalize the underlying
physics of wide-range of materials, including thermoelectrics. Thermoelectrics hold
immense potential for technological breakthroughs in power requirement for deep space
missions and waste-energy recovery and are being rapidly commercialized. In this talk, I
will present our combined experimental (inelastic neutron scattering, nuclear resonance
inelastic x-ray scattering, time-resolved x-ray scattering measurements from X-ray free
electron lasers) and theoretical studies (anharmonic phonon simulations) of
thermoelectric SnSe as a function of temperature, pressure, and photoexcitation1-4.
In the thermoelectric conversion of thermal gradients into useful electrical energy,
the figure of merit, zT=S2σT/κ correlates inversely with thermal conductivity, κ (S is the
Seebeck coefficient and σ the electrical conductivity). As κ in a semiconductor is
dominated by the lattice component, κlat, sustained efforts seek to design materials that
suppress phonon propagation.
In thermoelectric SnSe, zT is found to be exceptionally high close to the phase
transition at 805 K, which is driven by condensation of the lattice instability5,6. This
lattice instability can also be triggered by pressure and photoexcitation. We probe the
lattice instability as a function of temperature, pressure, and photoexcitation using
neutron, x-ray, and free-electron laser sources. Combining measurements with
anharmonic phonon simulations, we rationalize the thermal transport and consequently
high thermoelectric conversion efficiency in SnSe. Experimental and theoretical tools
used here have broad applicability and can be applied to, for example, ferroelectrics and
superionic conductors to decipher the origin of the spontaneous polarization and liquid-
like thermal transport7,8.
REFERENCES:
1. D. Bansal, J. Hong, C.W. Li, A.F. May, W. Porter, M.Y. Hu, D.L. Abernathy, and O. Delaire.
“Phonon anharmonicity and negative thermal expansion in SnSe.” Physical Review B, Vol. 94,
054307, 2016.
2. C.W. Li, J. Hong, A. May, D. Bansal, S. Chi, T. Hong, G. Ehlers, and O. Delaire. “Orbitally-
driven giant phonon anharmonicity in SnSe.” Nature Physics, Vol. 11, No. 12, pg. 1063-1069,
2015.
3. S. Yang, D. Bansal et al., Unpublished.
4. T. Lanigan-Atkins, D. Bansal et al., Unpublished.
5. L.-D. Zhao, G. Tan, S. Hao, J. He, Y. Pei, H. Chi, H. Wang, S. Gong, H. Xu, V. P. Dravid, C.
Uher, G. J. Snyder, C. Wolverton, and M. G. Kanatzidis, Science 351, 141, 2016.
6. L.-D. Zhao, S.-H. Lo, Y. Zhang, H. Sun, G. Tan, C. Uher, C. Wolverton, V. Dravid, and M.
Kanatzidis, Nature (London) 508, 373, 2014.
7. D. Bansal, J.L. Niedziela, R. Sinclair, V. Ovidiu Garlea, D.L. Abernathy, S. Chi, Y. Ren, H. Zhou,
and O. Delaire. “Momentum-resolved observations of the phonon instability driving geometric
improper ferroelectricity in yttrium manganite.” Nature Communications, Vol. 9, Article No. 15,
2018.
31
8. J.L. Niedziela,* D. Bansal,* A. May, J. Ding, T. Lanigan-Atkins, G. Ehlers, D.L. Abernathy, A.
Said, and O. Delaire. “Selective breakdown of phonon quasiparticles across superionic transition
in CuCrSe2.” Nature Physics, Vol. 15, pg. 73-78, 2019. (*co-first authors)
INVITED LECTURES: IL 16
Intermolecular Tuning of Non-Adiabatic dynamics via Hydrogen
Bonding G. Naresh Patwari,a
a Department of Chemistry, Indian Institute of Technology Bombay, naresh@chem.iitb.ac.in
The excited state dynamics in several hydrogen-bonded complexes of
phenylacetylene and its fluorinated analogues were investigated using electronic
spectroscopic methods. The fluorescence properties of these complexes could be
modulated by changing one of the hydrogen bonding partners, either by appropriate
fluorine substitution on the phenyl ring or by modifying its hydrogen bonding partner. For
example, in the case of phenylacetylene complex with methylamine two distinct hydrogen-
bonded isomers were observed. The first one is characterized by the presence of C–H∙∙∙N
hydrogen bond while the other one consists of N–H∙∙∙π hydrogen bonding. Interestingly,
the N–H∙∙∙π complex was fluorescent in nature, while the C–H∙∙∙N hydrogen-bonded was
non-fluorescent. The most interesting aspect of the phenylacetylene-methylamine complex
is the structure dependent fluorescence quenching behavior. Evidently, the formation of
the C–H∙∙∙N hydrogen-bonded complex leads to fluorescence quenching while the
fluorescence is observed for the N–H∙∙∙π hydrogen-bonded complex. Amines are known to
be effective quencher via the electron transfer mechanism. In the case of N–H∙∙∙π complex
lone pair electrons on the nitrogen atom are free and relatively at a closer distance from the
π electron cloud of the benzene ring, which carries the excitation, for effective quenching.
Contrary to such expectation, the N–H∙∙∙π complex was found to be fluorescent, while
fluorescence quenching is effective in the C–H∙∙∙N hydrogen-bonded complex, wherein the
lone-pair electrons are engaged in hydrogen-bond formation. In an effort to determine the
excited state dynamics of phenylacetylene and two of its methylamine complexes and to
rationalize the fluorescence quenching behavior, time-resolved picosecond pump-probe
experiments were carried out The single exponential fits to excited state decay profiles of
N–H∙∙∙π and C–H∙∙∙N complexes yield lifetime of 0.56 ns and 2.95 ns, respectively.
However, it is very surprising to note that the excited state lifetime of the fluorescent N–
H∙∙∙π complex (0.56 ns) is lower than the non-fluorescent C–H∙∙∙N complex (2.95 ns),
which is completely counterintuitive to normal quenching mechanism, including the
electron transfer quenching mechanism. Given the fact that the excited state lifetime of the
non-fluorescent C–H∙∙∙N complex is higher than the fluorescent N–H∙∙∙π complex, the
fundamental question that arises is the, “what is the nature of the excited state?” The
experimental observations can be rationalized on the basis of non-adiabatic dynamics
introduced due to hydrogen bonding.
32
INVITED LECTURES: IL 17
Origin of Slow Solvation Dynamics in DNA: What is the Biological
Significance? Sobhan Sen
Spectroscopy Laboratory, School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067,
sens@mail.jnu.ac.in
Water around biomolecules is special for behaving strangely both in terms of
structure and dynamics, while ions are found to control various interactions in
biomolecules such as DNA, proteins and lipids. The questions that how water and ions
around these biomolecules behave in terms of their structure and dynamics, and how they
affect the biomolecular functions have triggered tremendous research activities worldwide.
Such activities not only unfolded important static and dynamic properties of water and ions
around these biomolecules, but also the debate regarding their explanation and role in
biological functions. DNA being negatively charged, it interacts strongly with surrounding
dipolar water and positively charged counterions – leading to complex electrostatic
coupling of water and ions with the DNA. Recent time-resolved fluorescence stokes shift
experiments and related computer simulation studies from our group and other laboratories
have unfolded many unique features of slow water and ion dynamics near DNA. In this
talk, it will be discussed how combining results from time-resolved fluorescence Stokes
shifts experiments from femtoseconds to nanoseconds and large-scale atomistic molecular
dynamics (MD) simulation on DNA one can unfold unique dynamic features of perturbed
water and ions near DNA. In particular, it will be shown that unlike in proteins and lipids,
the coupled (solvation) dynamics of water, ions and DNA can lead to dispersed slow
relaxation over broad time over several decades, whose origin lies mainly with the
dynamically coupled DNA-water motions.1 It is also found that such slow solvation
dynamics can possibly link to the DNA base-mismatch specific dynamics, which may act
as qunique cues in ultrafast time-scale for mismatch specific DNA regognition by
mismatch-repair enzymes.2
REFERENCES:
1. D. Sardana, K. Yadav, H. Shweta, N. S. Clovis, P. Alam, S. Sen, J. Phys. Chem. B 2019 (DOI:
10.1021/acs.jpcb.9b09275).
2. H. Shweta, M. K. Singh, K. Yadav, S. D. Verma, N. Pal, S. Sen, J. Phys. Chem. B 2017, 121, 10735.
33
INVITED LECTURES: IL 18
Ultrafast photoelectron-photoion coincidence imaging spectrometer to
explore molecular chirality. Saurabh Shuklaa, Sagnik Dasa, Rishabh Tripathia, Vinod Kumara and N Bhargava
Rama* a Department of Physics, IISER Bhopal
*nbhargavram@iiserb.ac.in
We have recently commissioned a dual velocity map imaging spectrometer capable
of measuring photoelectrons and photoions in coincidence at IISER Bhopal to study
photoionization dynamics in polyatomic molecules and specifically chiral molecules in the
UV and VUV regime. It is now established that chiral molecular potential leads to
asymmetric scattering of photoelectrons upon ionization by left and right circular polarized
light [1, 2, 3]. The use of short femtosecond pulses in the UV and the VUV regime in
combination with an electron-ion spectrometer will provide us complete kinematic and
differential information. I will describe the capabilities of the newly-built spectrometer and
our recent measurements. I will also review some latest developments on photoelectron
circular dichroism research from across the world.
REFERENCES:
1. B. Ritchie, Phys Rev A 13, 1411 (1976)
2. I Powis, Adv, in Chemical Physics 138, 267 (2008)
2. C S Lehmann, N Bhargava Ram, I Powis and MHM Janssen, J Chem Phys 139, 234307 (2013)
34
INVITED LECTURES: IL 19
Real-Time Four-Dimensional Spatio-Temporal Terahertz Imaging
using Intense Terahertz Pulse
Mukesh Jewariya,
CSIR-National Physical Laboratory-New Delhi-110012
E.mail: jewariya.mukesh@nplindia.org
We demonstrated four-dimensional spatio-temporal (4D-ST) terahertz (THz) imaging and
its applications for THz tomography, THz spectral imaging, and THz spectral computed
tomography (CT). The 4D-ST THz imaging enables to achieve incompatible high-speed
data acquisition. 3D THz reflection tomography is effectively used to visualize internal
structure of an object whereas 4-D image is its chemical composition.
In the recent years THz imaging with pulsed THz radiation has emerged an innovative tool.
The first demonstration of THz imaging was reported in 1995 by Hu et.al [1-3], later
several other THz imaging techniques have been reported by many other authors like
reflection tomography [4], spectral imaging [5], and computed tomography (CT) [6]. In
THz tomography the internal structure of the sample can be easily visualized by the
distribution of the group refractive index. This technique adopts a time-of-flight
measurement of THz echo pulses. In this method THz pulse is incident upon the sample in
transmission or reflection geometry. The commercially available method such as
ultrasound and X-ray need a “contact” for investigation and these are “invasive”. There is
a potential of damage and only external imaging information is obtained whereas THz
wave acts as a non-contact and non-invasive probe and obtain its internal structure and
chemical composition.
The 3D THz CT system is based on an amplified Ti:Sapphire laser with 1 kHz repetition
rate, 0.8 mJ/pulse, 800 nm central wavelength and 150 fs pulse duration. To perform fast
3D THz CT, the sample is set vertically (Y-axis) and first horizontally scanned with a
constant speed of 2 mm/s along the X-axis so that a whole 2D-ST image set can be acquired
for a given projection angle. Finally, for each projection angle and at every horizontal and
vertical sample positions, the pixel value is extracted by measuring the peak-to-peak value
of the THz temporal waveform pulse. After FFT of temporal data, the spectral amplitude
at a given frequency could also be extracted for spectral imaging [8]. Then, the application
of the well-known filtered backprojection (FBP) algorithm implemented in the ImageJ
software will numerically provide the multiplanar slices of the sample in order to finally
reconstruct the 3D volume [9]. The temporal data extracted from it added extra dimension
and tells about its chemical composition. This added temporal profile is the 4th dimension.
It is well-known that FBP suffers from several drawbacks such as beam hardening, which
can induce cupping, streaks and blurring because rays from some projection angles are
hardened to a differing extent than rays from other angles, confusing the reconstruction
algorithm. To reduce this phenomenon, it is important to record at least 36 projections. Of
35
course, depending on maximum data storage and acquisition time fixed by the operator, it
is also possible to record 72 projections with a 2.5° angle step. However, we considered
that the best compromise between reconstruction quality (contrast, intensity and geometric
preservation) and acquisition time consists in recording only 36 projections [10].
The main advantage of the proposed method relies on real-time THz line projection
providing 10 ms acquisition time of 2D-ST THz image. Therefore, 3D THz CT has been
performed in only a few minutes, representing a significant improvement compared with
common systems, which can be powerful for sensing, non-destructive inspection and
material characterization in real world applications.
REFERENCES:
[1] D. M. Mittleman, Sensing with THz radiation. Berlin: Springer, 2003.
[2] M. Tonouchi, “Cutting-edge terahertz technology,” Nature Photon., vol. 1, no. 2, pp. 97 – 105, Feb.
2007.
[3] B. B. Hu and M. C. Nuss, “Imaging with terahertz waves,” Opt. Lett., vol. 20, iss. 16, pp. 1716-1718,
Aug. 1995.
[4] D. M. Mittleman, S. Hunsche, L. Boivin, and M. C. Nuss, “T-ray tomography,” Opt. Lett., vol. 22, iss.
12, pp. 904-906, Jun. 1997.
[5] T. Löffler, T. Bauer, K. Siebert, H. Roskos, A. Fitzgerald, and S. Czasch, Opt. Express, vol. 9, iss. 12,
pp. 616-621, Dec. 2001.
[6] B. Ferguson, S. Wang, D. Gray, D. Abbott, and X.-C. Zhang, Opt. Lett., vol. 27, iss. 15, pp. 1312-
1314, Aug. 2002.
[7] A. J. Fitzgerald, B. E. Cole, and P. F. Taday, J. Pharm. Sci., vol. 94, no. 1, pp. 177-183, Jan. 2005.
[8] W.L. Chan, J. Deibel, and D. M. Mittleman, Rep. Prog. Phys. 70, 1325–1379 (2007).
[9] G. T. Herman, Image Reconstruction From Projections: The Fundamentals of Computerized
Tomography (Academic Press Inc., 1980).
[10] E. Abraham, A. Younus, C. Aguerre, P. Desbarats, and P. Mounaix, Opt. Comm. 283(10), 2050-2055
(2010).
36
Stabilization and sensing of G-quadruplex DNA structures with
indolylquinolinium based probes
Annyesha Biswas,a and Pradeepkumar P.I.* b a Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, India,
annyeshabiswas123@gmail.com
b Professor, Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, India,
pradeepkumarpi@gmail.com
G-quadruplexes (G4s), four stranded motifs formed by G-rich DNA/RNA
sequences of the genome or transcriptome and harbour significant biological importance.1
Owing to their dynamic existence and polymorphic nature, specific recognition of G4
structures by small molecule ligands is challenging.2 The ligands, which could turn-on
fluorescence upon interaction with G4 structures provide a powerful and direct tool for
their direct detection inside the cells.3,4 Towards this end, we report the synthesis of
fluorescent probes based on indolylquinolinium moiety, which are expected to have the
potential to stabilize and sense cellular G4 structures with high target selectivity and
specificity. CD melting experiments have shown, the best molecule InQEtPy acts as a G4
stabilizer with preferential stabilization of parallel topology of promoter c- MYC and c-
KIT1 G4s, over telomeric G4 and duplex DNAs. Fluorimetric titration data revealed ~10
fold fluorescence enhancement on interaction with c-MYC G4 structures. TCSPC
experiments of the dye in unbound state showed relatively faster lifetime than the bound
state with different DNAs with two excited state lifetime possibly indicating two binding
modes.The findings of this research work are expected to provide new fluorescent turn-on
probes for G4 nucleic acids, which could be utilized for diagnostic applications.
REFERENCES 1. Bochman, M.L.; Paeschke, K.; Zakian, V.A., DNA secondary structures: stability and function of G- quadruplex structures, Nature Reviews Genetics, 13, 770–780 (2012) 2. Hertsch, R.H.; Antonio, M.D.; Balasubramanian, S., DNA G-quadruplexes in the human genome: detection, functions and therapeutic potential, Nature Reviews Molecular Cell Biology ,18, 279–284 (2017) 3. Mohanty, J.; Barooah, N.; Dhamodharan, V.; Harikrishna, S.; P. I. Pradeepkumar.; Bhasikuttan, A.C.,Thioflavin T as an Efficient Inducer and Selective Fluorescent Sensor for the Human Telomeric G-Quadruplex DNA, J. Am. Chem. Soc., 135, 367−376 (2013) 4. Zhang, S.; Sun, H.; Wang, L.; Liu, Y.; Chen, H.; Li, Q.; Guan, A.; Liu, M.; Tang, L. Real-time Monitoring of DNA G-quadruplexes in Living Cells with a Small-molecule Fluorescent Probe, Nucleic Acids Res. 46, 7522-7532 (2018)
Figure 1.G- quadruplex
sensing by small
molecule ligand
37
Enzyme product releasing mechanism under piconewton force manipulation: A
single molecule investigation using photon time-stamping spectroscopy
Nibedita Pal, a Meiling Wu,b and H. Peter Lu*b
a Present address: Indian Institute of Science Education and Research (IISER) Tirupati, Andhra Pradesh
517507, India
b Department of Chemistry, Center for Photochemical Sciences, Bowling Green State University, Ohio
43403, USA
*hplu@bgsu.edu
The exploration of the conformational fluctuation of an enzyme during catalytic event has
significance implication in the field of enzymology. However, monitoring the
conformational fluctuation of an enzyme during essential steps of a catalytic reaction is
challenging due to transient nature of the intermediates. Using single molecule total
internal reflection fluorescence microscopy (TIRFM) guided confocal photon time-
stamping spectroscopy we have interrogated the conformational dynamics of Horseradish
Peroxidase enzyme. A nascent formed fluorogenic product is used as a probe reporting the
active site conformational behavior. We have unraveled the presence of complex
conformations during product release and the effect of mechanical perturbation on it.
38
Polyethylene glycols affect electron transfer rate in phenosafranin-DNA
Partha Pyne,a Nirnay Samanta,a Animesh Patra,a Aritra Das,b Pratik Sen,b Rajib Kumar
Mitraa aDepartment of Chemical, Biological and Macromolecular Sciences, S N Bose National Centre for Basic
Sciences, Block-JD, Sector-III, Salt Lake, Kolkata-700106, India; parthapyne@bose.res.in bDepart of Chemistry, Indian Institute of Technology Kanpur, Kanpur – 208 016, India
Real cellular environments are crowded to almost 40% of the total volume. It stands
interesting to study electron transfer (ET) rate during drug-DNA interaction in crowded
milieu. We have studied the emission characteristics of phenosafranine (PSF) intercalated
to calf thymus DNA in the presence of polyethylene glycols (PEGs) of different chain
lengths. The emission of PSF quenches severely when intercalated to DNA; the quenching
is released upon the addition of PEGs. The structural conformation of the CT DNA has
been established using circular dichroism spectroscopy. ps-resolved fluorescence
measurements reveal significant decrease in the contribution of the DNA induced quenched
time-constant of PSF upon the addition of PEGs, however, fs-resolved measurements show
nominal changes in the time constants. Our study shows that the electron hopping rate
through the guanine base in DNA core remains unaffected whereas the ‘through space’ ET
process is affected in the presence of crowders.
Fig a) Representative CD signal of DNA under PEG200. b) Plot of Tm with PEG
concentration. c) Representative fluorescence intensity of PSF under different PEG20
concentration. Relative fluorescence intensity under complete intercalating condition
(inset). d) Relative contribution of faster component with PEG concentration.
[PEG] (% W / V)0 5 10 15 20 25 30
Tm
(0C
)
55
60
65
70
75
80 EG
PEG200
PEG400
PEG1000
(b)
Wavelength (nm)
220 240 260 280
Elli
pticity (
mdeg
)
-12
-8
-4
0
4
8
DNA
10%
20%
30%
(a)
[PEG] (%W/V)
0 10 20 30
Rel. c
ontr
. of
fa
ste
r
0.0
0.2
0.4
0.6
0.8
1.0
EG
PEG200
PEG400
PEG1000
(d)
Wavelength (nm)
540 570 600 630 660
Flu
ore
scence I
nte
nsity (
a.u
)
0
2
4
6
8
10
Water
0%
10%
20%
30%
(c)
[PEG] (%W/V)
0 5 10 15 20 25 30
1
10
Rel. int.
EGPEG200 PEG400 PEG1000
39
Investigation on the ESPT Dynamics of D-Luciferin in Aqueous trifluoroethanol
and ethanol Mixtures Sk Imadul Islam1, Sumana Pyne1, Debasish Das Mahanta1, Souradip Dasgupta3, Anindya
Dutta3, Dipak Kumar Palit2 and Rajib Kumar Mitra1
1 Department of Chemical, Biological & Macromolecular Sciences, S. N. Bose National Centre for Basic
Sciences, Block JD, sector-III, Salt Lake, Kolkata-700106, INDIA, e-mail: imadulislam@bose.res.in 2 UM-DAE Centre for Excellence in Basic Sciences, Mumbai University, Kalina Campus, Santacruz (E),
Mumbai 400098, INDIA 3 Department of Chemistry, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, INDIA
Proton transfer in binary mixture solvent has received much attention in the field of
chemistry and biology as biological proton transfer reactions ususlly take place in the
interfaces and liquid mixture can often reproduce such platform.1,2 We have investigated
intermolecular excited-state proton transfer (ESPT) of firefly’s chromophore D-luciferin
in two different aqueous-alcohol binary mixtures (ethanol, EtOH-water and
trifluoroethanol, TFE-water) using steady-state and ps as well as fs-resolved fluorescence
spectroscopic techniques. We aim to understand the differences of H-bonding affinity of
EtOH and TFE with water and its subsequent effect on the ESPT mechanism in these two
mixtures. We observe contrasting behaviour in emission intensity, fluorescence quantum
yield, fluorescence lifetime, radiative/non-radiative decay constant and ESPT kinetics of
both the forms (protonated and deprotonated) of D-luciferin in these two alcohol-water
binary mixtures. We have found that ESPT kinetics of D-luciferin in EtOH-water is faster
than that in TFE-water mixture. It increases near-linearly with Xw (mole fraction of water
in the mixture) in EtOH while in TFE the change is not linear. From the time-resolved
emission measurements at different wave lenghts, we construct the time resolved area
normalized emission spectra (TRANES) and find an iso-emissive point for TFE-water
system (upto Xw=0.6) while it is not evident in EtOH-water mixture. We infer that the
solvation dynamics and ESPT kinetics are comparable in EtOH while it is not so in TFE-
water mixture.
REFERENCES
1. Cohen, B.; Martin Álvarez, C.; Alarcos Carmona, N.; Organero, J. A.; Douhal, J Phys. Chem. B
2011, 115, 7637-7647.
2. Simkovitch, R.; Shomer, S.; Gepshtein, R.; Shabat, D.; Huppert, J Phys. Chem. A, 2014, 118,
1832-1840
40
Formation of Long Lived Triplets through Singlet Fission in Lycopene Aggregates
Arup Kundu, Jyotishman Dasgupta* Department of Chemical Sciences, 1 Homi Bhabha Road, Tata Institute of Fundamental Research, Mumbai
400005, India. Carotenoids are natural conjugated chromophores that efficiently harvest light
through singlet states as well as form photo-protective machinery in photosynthesis
through the formation of nascent triplet states.1 In recent years these chromophores have
been used in organic photovoltaic devices as materials for high-quantum yield triplet
generation through a process called singlet fission (SF). Singlet fission is a process by
which two triplets can be generated at the cost of one photon through an intermediate
singlet state which has a multi-excitonic triplet-triplet character localized over two distinct
molecules.2 It is however a challenge to stabilize these triplet states formed through SF for
utilization as charge carriers since they tend to recombine to re-form the parent singlets.
Here we use lycopene, a major plant carotene to demonstrate that tuning the aggregate
structures enables efficient singlet fission with long-lived triplet states. We prepared
lycopene H-aggregates from organic solution and probed the photoexcited dynamics using
femtosecond transient pump-probe spectroscopy in conjunction with steady-state
resonance Raman spectroscopy. Through a detailed kinetic analysis we confirmed the
emergence of a correlated triplet pair in 20 ps timescale which subsequently lead to the
formation of long lived triplet sate with lifetime of 155 μs.3 We envision that our results
provide a facile access to long-lived triplets and may have a potential application in organic
photovoltaics.
REFERENCES
1. a) Horton, P.; Ruban, A. V.; Walters, R. G. Regulation of Light Harvesting in Green Plants. Annu. Rev.
Plant Physiol. Plant Mol. Biol., 1996, 47, 655−684; b) Frank, H. A.; Cogdell, R. J. Carotenoids in
Photosynthesis. Photochem. Photobiol. 1996, 63, 257−264; c) Pascal, A. A.; Liu, Z.; Broess, K.; van Oort,
B.; van Amerongen, H.; Wang, C.; Horton, P.; Robert, B.; Chang, W.; Ruban, A. Molecular Basis of
Photoprotection and Control of Photosynthetic Light harvesting. Nature, 2005, 436, 134−137.
2. a) Wang C. and Tauber M. J., High-Yield Singlet Fission in a Zeaxanthin Aggregate Observed by
Picosecond Resonance Raman Spectroscopy, J. Am. Chem. Soc, 2010, 132, 13988–13991; b) Musser A. J.,
Maiuri M., Brida D., Cerullo G., Friend R. H.,and Clark J., The Nature of Singlet Exciton Fission in
Carotenoid Aggregates, J. Am. Chem. Soc. 2015, 137, 5130−5139; c) Smith M. B., and Michl J. Singlet
Fission, Chem. Rev. 2010, 110, 6891–6936.
3. A. Kundu and J. Dasgupta; to be submitted
41
Conformational Dynamics of c-MYC Promoter based i-Motif DNA in Crowded
Environments
Sneha Paul, Sk Saddam Hossain, Anunay Samanta a School of Chemistry, University of Hyderabad, Gachi Bowli, Hyderabad-500046,
sneha.paul0027@gmail.com
Cytosine-rich DNA sequences fold into secondary structures called i-Motifs, which are
usually stable at acidic pH.1 However, molecular crowding agents like polyethylene glycol
(PEG) are known to facilitate the formation of these structures even at neutral pH.2 As
crowding mimics the intracellular environment and not much is known about the folding
pathway of i-Motifs in such constrained condition, we have probed in detail the
conformational dynamics of a 22-mer c-MYC promoter based C-rich sequence (Py22) in
presence of PEG, employing single-molecule Förster resonance energy transfer (smFRET)
and fluorescence lifetime measurements. We find that the conformational change is not a
simple two-state transition (as observed in ensemble measurements) between a random coil
and folded i-Motif structure. Rather, it involves a partially folded conformation as
intermediate where the bases are not as efficiently stacked as in completely folded i-Motif.
The relative population of each species is found to be governed by the size and
concentration of PEG and 30% (w/w) PEG6000 is the optimum condition for the folding
of Py22. Under this condition, ~ 80% of Py22 exists in the fully folded i-Motif form and ~
15% of it is in the partially folded state.
REFERENCES
1. H. A. Assi, M. Garav, C. Gonzalez, M. J. Damha, Nucleic Acids Res. 2018, 46, 8038.
2. J. Cui, P. Waltman, V. H. Le, E. A. Lewis, Molecules 2013, 18, 12751.
42
Solvation dynamics in solvent free protein – polymer surfactant biomolecular assemblies
Tanuja Kistwala, Anasua Mukhopadhyaya, Kamendra Sharmaa, and Anindya Dattaa
a Department of Chemistry, Indian Institute Of Technology Bombay, Powai, Mumbai 400076,India
Solvent-free proteins have attracted tremendous attention in recent times, due to its
potential use as a green, nonaqueous solvent with low-volatility, for the synthesis of an
organic and inorganic compounds, as electrolytes, catalysis, etc.1,2 While dynamics of dye
labelled HSA has been reported3,4,5, We focus on solvation dynamics of solvent-free
protein, labelled with CPM dye (7-dimethylamino-3-(4-maleimidophenyl)-4-methyl-
coumarin to understand bound water dynamics. This study has been done using
Fluorescence correlation spectroscopy (FCS) with a conformational dynamics model of
data analysis and also a comparitive examination of hydrodynamic radii of different CPM
labelled HSA modified system. Solvent free causes blue shift in the emission maxima from
CPM covalently bound to HSA. The average solvation time is increased from 700 ps (CPM
bound to HSA) to 2 ns in presence of solvent free CPM labelled HSA. FCS suggest that in
solvent free system, diffusion coefficient decreases and hydrodynamic radius increases
which implies larger protien size.
REFERENCES
1. A. Mukhopadhyay, T. Das, A. Datta and K. P. Sharma, Biomacromolecules, 2018, 943–950, 19.
2. F. X. Gallat, A. P. S. Brogan, Y. Fichou, N. McGrath, M. Moulin, M. Härtlein, J. Combet, J.
Wuttke, S. Mann, G. Zaccai, C. J. Jackson, A. W. Perriman and M. Weik, J. Am. Chem. Soc., 2012,
13168–13171, 134.
3. U. Mandal, S. Ghosh, G. Mitra, A. Adhikari, S. Dey and K. Bhattacharyya, Chem. - An Asian J.,
2008, 1430–1434, 3.
4. D. K. Sasmal, T. Mondal, S. Sen Mojumdar, A. Choudhury, R. Banerjee and K. Bhattacharyya, J.
Phys. Chem. B, 2011, 13075–13083, 115.
5. S. K. Pal, J. Peon and A. H. Zewail, Proc. Natl. Acad. Sci., 2002, 1763–1768, 99.
43
Solute and Solvent Dynamics in Neat, and Wet-Octanol: Steady State and Time
Resolved Fluorescence Measurements
Narayan Chandra Matiy, Kajal Kumbhakar, Ranjit Biswas Chemical Biological and Macromolecular Sciences (CBMS)
S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata 700106 India E-
mail: ranjit@bose.res.in
Neat 1-octanol and wet-octanol has been the subject of numerous studies due to
their property of membrane mimics.1-3Interaction and dynamics of different external
fluorescent solutes in neat and wet-octanol and as well as solvent dynamics have been
investigated via steady state and time-resolved fluorescence (TRF) measurements in the
temperature range of 283≤T/K≤323 with various mole fraction of water (XH2O = 0 to 0.20)
in the octanol rich region. Coumarin 153 (C153), Coumarin 343 (C343), trans-2-[4'-
(dimethylamino)styryl]benzothiazole DMASBT have been employed to investigate solute-
centre reactive and non-reactive relaxation dynamics in this aqueous mixture. Excitation
wavelength dependence of fluorescence emissions4,5 suggest that both the neat and aqueous
binary mixtures, within the lifetime of C343 (<life > 3-4 ns)6 and DMASBT (<life > 0.5
ns),7 are spatially heterogeneous. Fluorescence anisotropy studies with C153 and C343 in
neat and wet-octanol have been used to explore the solute-medium frictional coupling.
Inspite of nearly same size, rotation dynamic of C153 shows fractional viscosity
dependence while C343 nearly follows the Stoke-Einstein-Debye model. Dynamic
fluorescence stoke shift measurements detected fast (sub-nanosecond) and slow
(nanosecond) solvent relaxation time scale in these media.
REFERENCES
1. 1. S. E. Debolt, P. A. Kollman, J. Am. Chem. Soc. 1995, , 5316-5340, 117.
2. S. A. Best, K. M. Merz, C. H. Reynolds, J. Phys. Chem. B 1999, 714-726, 103.
3. J. L. MacCallum, D. P. Tieleman, J. Am. Chem. Soc. 2002, 15085-15093, 124.
4. Z. Hu, C. J. Margulis, PNAS 2006, 831-836, 103(4).
5. P. K. Mandal, M. sarkar, A. Samanta, J. Phys. Chem. B 2004, 9048-9053, 108.
6. S. Koley , H. Kaur and S. Ghosh, Phys. Chem. Chem. Phys. 2014, 22352, 16.
7. M. Kondo, X. Li, M. Maroncelli, J. Phys.Chem. B 2013, 12224–12233, 117.
44
Ultrafast Control for Perfumery Industries
Rohit Goswami,a Ashwini Kumar Rawat, b Debojit Chakrabarty,c Debabrata Goswamid a Department of Chemistry, IIT Kanpur, rgoswami@iitk.ac.in, a Department of Chemistry, IIT Kanpur, rashwini@iitk.ac.in b Head R&D and Quality, Jyothy Laboratories Ltd., debojit.chakrabarty@jyothy.com
c Faculty of Chemistry, IIT Kanpur, dgoswami@iitk.ac.in
The thermal lens (TL) effect is governed by the refractive index changes in a semi-
transparent medium and the subsequent competition between the convective and
conductive modes of heat dissipation1. Recent studies2 have shown the utility of this effect
as a probe for complex systems. The signal in alcohols3 is notable as it establishes a strong
correlation between the TL signal and physical properties, like mobility, steric effects, and
hydrogen bonding. The perfumery industries, unlike the rest of the chemical process
industries, remain largely untouched by the scientific community. The ‘accords’ or
perfumery primitives are still generated by manual labor, though a qualitative analysis of
perfumes is defined4 by the pyramid shown in Fig. 1. Quantitative estimators are few and
far apart, as empirical correlations like the odor value4 (OV) have to typically account for
variations in sociological conditions such and geography, gender and require a large
number of trained human specialists. The intractable complexity of multi-component
mixture analysis5 precludes the ability of the equation of state (EOS) methods to aid the
industry. Leveraging thermal lens effects as a control parameter obtained from our ultrafast
laser experiments, we have found a clear correlation between our TL data and are able to
use this as a quantitative measure to determine the optimal accord concentration. This shall
be of immense use to the perfumery industries, and also provides key insights into the
interplay of light-matter interactions.
Figure 1: The qualitative approach to traditional perfumery analysis4 where the
notes are analysed by odor-value correlations.
REFERENCES
1. I. Bhattacharyya, P. Kumar, D. Goswami, J. Phys. Chem. B, 2011, 115, 2
2. S. Singhal, S. Goswami, A. Banerjee, D. Goswami 2019 URSI AP-RASC 2019.
3. P. Kumar, S. Dinda, A. Chakraborty, D. Goswami, Phys. Chem. Chem. Phys. 2014, 16, 24.
4. M. A. Teixeira, O. Rodriguez, P. Gomes, V. Mata, A. Rodrigues, Oxford, England: Butterworth-
Heinemann 2012.
R. Taylor, R. Krishna, Taylor, John Wiley & Sons 1993.
45
Unveiling the Effect of Sugars on Dynamics of Different Fluorophores in the
Interior of Aerosol OT Lamellar Structures: From Picosecond-to-Femtosecond
Study
Meghna Ghosh, Rupam Dutta, Arghajit Pyne, Nilmoni Sarkar*
Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, WB, India.
E-mail: nilmoni@chem.iitkgp.ac.in and nilmonisarkar1208@gmail.com
The anionic surfactant aerosol OT (AOT) can self-aggregate to produce
microheterogeneous confined assemblies such as reverse micelles (RMs) and lamellae
which can potentially mimic biological interfaces like cell membranes etc. On the other
hand, sugar molecules can stabilize biomembranes against extreme temperature changes.
In this study, we have performed a combination of steady-state and time-resolved
fluorescence measurements using three Coumarin dyes having significantly different
hydrophobicity to unveil the location of the sugars (sucrose and sucralose) and their
interactions with the lamellar structures. Our study reveals that sucrose molecules are
mostly present in the interfacial region whereas the most probable location of sucralose is
the interior of the AOT bilayer. This study provides an interesting aspect about the location
of two structurally similar sugar molecules inside the lamellae and their effect on the
dynamics of different Coumarin dyes.
REFERENCES
1. R. Dutta, M. Ghosh, A. Pyne, N. Sarkar J. Phys. Chem. B 2019,123, 117. 2. N. Nandi, K. Bhattacharyya, B. Bagchi Chem. Rev. 2000, 100, 2013.
3. D. De, A. Datta Langmuir 2013, 29, 7709.
46
Use of Dimeric Excited States of the Donors in D4-A Systems for Accessing White
light Emission, Afterglow and Invisible Security Ink
Harsh Bhatia,a Debdas Rayb
aDepartment of Chemistry, Shiv Nadar University, NH-91, Tehsil Dadri, Gautam Buddha Nagar, Greater
Noida, Uttar Pradesh, 201314, India
b Faculty of Chemistry, Shiv Nadar University, NH-91, Tehsil Dadri, Gautam Buddha Nagar, Greater
Noida, Uttar Pradesh, 201314, India, debdas.ray@snu.edu.in
Pure organic white light emitters with persistent room temperature
phosphorescence (RTP) feature have unique advantages and various potential applications.
However, the studies of single-component organic white light emitters with AG and visible
light excitation (VLE)-dependent efficient RTP features remain a challenging area of
research in photophysics. Herein, we synthesized three terephthalonitriles in which 2,3,5,6-
positions are covalently attached to 2-fluoro-phenoxy (TOF), 2-chloro-phenoxy (TOC),
and 2-methoxy-phenoxy groups (TOM)1 to give twisted geometries. We observed that
powder samples of both TOC and TOM show white light emission with CIE coordinates
of (0.32, 0.38) and (0.26, 0.33), respectively, while TOM gives VLE-dependent efficient
RTP under ambient conditions. In addition, both TOC and TOF exhibit a dim AG feature.
Spectroscopic studies reveal that emission of these chromophores originates via radiative
decay of monomeric excited states (singlet, triplet), dimer-like excited states (DLES)
(singlet, triplet), and aggregated triplet states. Detailed spectroscopic and X-ray analyses
reveal the signature of DLES that is formed via conformational reorganization of the
phenoxy donors in the excited states. Single-crystal X-ray diffraction analysis shows that
the multiple lp(O)···π(C≡N)/C≡C, Cl/F···π, and hydrogen-bonding interactions in the X-
ray structures play a significant role in facilitating intersystem crossing2, stabilizing
multiple triplet states, and suppressing nonradiative decay, thereby triggering dim
afterglow under ambient conditions. We found that TOC and TOF exhibit persistent RTP
with lifetimes of 139 and 736 ms, respectively, when embedded in polyvinyl alcohol
matrix. Given the persistent RTP feature, invisible security ink application is developed.
These results provide a strategy to design white light-emitting materials with afterglow and
visible light-activated efficient RTP features.
REFERENCES
1. H. Bhatia, D. Ray, DOI: 10.1021/acs.jpcc.9b07762.
M. A. El-Syed, J. Chem. Phys. 1963, 38, 2834.
47
Origin of Slow Solvation Dynamics in DNA: DAPI in Dickerson-DNA
Deepika Sardana, Kavita Yadav, Him Shweta, Ndege Simisi Clovis, Parvez Alam,
Sobhan Sen*
School of Physical Sciences, Jawaharlal Nehru University,
New Delhi, India
Email: sens@mail.jnu.ac.in
Time-resolved fluorescence Stokes shift (TRFSS) experiments measure dynamics of
complex biomolecules and their surrounding environment from femtoseconds to
nanoseconds. These
experiments unravel
anomalously slow solvation
dynamics in DNA beyond
~100 ps, whose origin remains
incomprehensible. We
compare results of TRFSS
experiments to MD
simulations of minor groove-
bound DAPI in Dickerson-
DNA over five decades of
time from 100 fs to 10 ns.1 We
show the solvation time-
correlation function (TCF)
calculated from (200 ns)
simulation trajectory captures
most features of slow
dynamics, as measured in
experiment. Decomposition
of TCF into components
resolves that slow dynamics originate from dynamically coupled DNA-water motion. This
dynamically coupled DNA-water motion dominate in the slow solvation relaxation when
probed by minor groove-bound DAPI in Dickerson-DNA, although the effect of water-Na+
coupled motion on slow dynamics cannot be overlooked. We find that freezing DNA
fluctuations in simulation eliminates slower dynamics beyond ~100 ps, where water and
Na+ dynamics become faster, although signature of strong anti-correlation is captured.
Results show that primary origin of slow dynamics lies within slow fluctuations of DNA-
parts which perturb nearby water and ions to govern the slow concerted solvation dynamics
in Dickerson-DNA.
REFERENCES:
[1] Verma, S. D.; Pal, N.; Singh, M. K.; Sen, S. Sequence- Dependent Solvation Dynamics of Minor-Groove
Bound Ligand inside Duplex-DNA. J. Phys. Chem. B 2015, 119, 11019-11029.
Figure 1. Left - Snapshot from MD simulation showing 22 water
molecules and 3 Na+ which reside within 4 Å from the DAPI in
minor-groove of Dickerson-DNA scales at a probe-site inside
biomolecule (blue probe-molecule inside groove of DNA). Purple
and green balls represent ions. Right- Comparison of absolute Stokes
shifts of DAPI in Dickerson-DNA calculated from TRFSS
experiments and simulation. And inset shows Linear response
decomposition (LRD) of total simulated TCF(white) into partial-
TCFs of water (blue), DNA (green), Na+ (red) and Cl (purple)
48
[2] Sardana, D.; Yadav, K.; Shweta, H.; Clovis, N. S.; Alam, P, Sen, S. Origin of Slow Solvation Dynamics
in DNA: DAPI in Minor Groove of Dickerson-DNA. (Manuscript Submitted)
49
Impact of Urea on Structure and Dynamics of an Ionic Deep Eutectic Solvent:
Exploration through Reactive and Non-Reactive Solute Centered Dynamics
Arnab Sil,Sirshendu Dinda,Ranjit Biswas
Department of Chemical Biological & Macromolecular Sciences Technical Research Centre
S.N.Bose National Centre For Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata-700106
E-mail: ranjit@bose.res.in
We have prepared electrolyte and amide based deep eutectic solvents (DES)
where both acetamide and urea have been used as amide source. The effect of urea on the
structural and dynamical heterogeneities in these DESs have been studied in detail by
both steady state and time-resolved fluorescent measurements of fluorescent solute
coumarine153 (C153)1. The result shows strong decoupling of viscosity from diffusion
for all the DESs studied and addition of urea does not modify this decoupling. The
decoupling in these DESs is attributed to the presence of structural and dynamical
heterogeneities2. After characterizing these DESs, we have applied these DESs medium
to study the medium impact on photo induced trans to cis isomerisation of trans- 2-[4’-
(Dimethylamino) styryl] benzothiazole (DMASBT). It has been observed that presence of
urea does not alter the rate of reaction but addition of electrolyte (keeping the amide
percentile constant in the DESs) enhances the photochemical reaction.
REFERENCES
1. Manuscript under preparation: Sirshendu Dinda, Arnab Sil, Ranjit Biswas
2. M. D. Ediger, C. A. Angell and S. R. Nagel, The Journal of Physical Chemistry 1996,
13200-13212 ,100 (31).
3. M. Kondo, X. Li, M. Maroncelli, J. Phys.Chem. B 2013, 12224–12233, 117.
50
Solvation Dynamics in Mycobacterial Membranes Probed by Time-Resolved
Laurdan Fluorescence
Pranav Adhyapaka, Shobhna Kapoora a Department of Chemistry, Indian Institute of Technology Bombay, shobhnakapoor@chem.iitb.ac.in
Mycobacterium Tuberculosis serves as an epitome of how lipids—next to
proteins—can be utilized as central effectors in pathogenesis and arduously construct an
excellent barrier against most drugs.1-2 Aptly, mycobacteria use substantial amount of its
genome to synthesis atypical long (C60–90) chained and branched lipid molecules and
employs an array of specialized protein machinery to localize these lipids to distinct spatial
locations, inner (IM) and outer membrane (OM). The hydration properties of the lipid
membrane are highly essential for cell membrane activity ranging from regulating protein
function to lipid diffusion and drug transport3 and the significance of same especially in
structurally unique mycobacterial membranes remain hitherto unknown. By combining
steady state and time-resolved fluorescence using solvatochromic lipid probe Laurdan, we
have obtained unprecedented insights into the solvation dynamics of these unusual lipid
assemblies. Further we compare the behavior of mycobacterial lipids with eukaryotic
phospholipids thus elucidating the role of long acyl chains and branches in the lipid
structure on solvation properties. Finally, with fluorescence recovery after photobleaching
(FRAP), we correlate the water hydration dynamics to diffusion of lipids within
mycobacterial membranes. Investigating the solvation properties of the inner and outer
membrane lipids in a systematic manner presents a golden opportunity to deepen our
understanding of these spatially and compositionally distinct membrane platforms and their
plausible functional roles in bacterial survival, drug resistance, and pathogenesis.
REFERENCES
1. M. Mishra, S. Kapoor. Scientific Reports. 2019. https://doi.org/10.1038/s41598-019-49343-2
2. M. Siegrist, CR. Bertozzi. Cell Host Microbe. 2014, 15, 1-2.
3. P. Adhyapak and S. Kapoor. J Membrane Biol. 2019. https://doi.org/10.1007/s00232-019-00087-0
51
MODULATING INTERACTION MECHANISM OF DUPLEX DNA WITH
GRAPHENE OXIDE EMPLOYING TWO DIVERSE BINDERS
Sangita Kundu, Nilmoni Sarkar* Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur 721302, WB, India
E-mail: sangitakundu13@gmail.com
Aside from the conventional genetic roles, double stranded DNA molecules (dsDNA) are
employed in versatile applications in the field of the chemistry, biology and medical. The
amalgamation of these molecules with the graphene based nanomaterials making them
more potent in the biomedical, sensing and bioimaging applications. Here, we have
successfully explored the strong interaction of duplex DNA with graphene oxide (GO) and
the detailed analysis of the photophysical behaviour has been carried out using two
different DNA binding probes. The rotational and translational diffusion properties of these
fluorophores in presence of this DNA-GO bioconjugate are different depending on the
preferential location inside the DNA helix. Ultrafast spectroscopy has been employed to
elucidate the quenching mechanism of the two dye labeled DNA in presence of GO.
Furthermore, conformational alteration of dsDNA in presence of intercalator, EB
(Ethidium Bromide) and groove binder, DAPI (4'-6-diamidino-2-phenylindole) facilitate
the unusual restricted interaction of duplex DNA with GO. Our present finding can provide
a deep understanding of the unusual interaction between duplex DNA and GO. This
nanostructured biointerface material can be used as the potential candidate in cell imaging,
drug delivery and biosensing in near future.
Figure 1. Structural deformation of DNA in presence of GO and the effect on the dynamics
and diffusion properties of dye bound DNA in presence of GO.
REFERENCES
1. X.Zhao. J. Phys. Chem. C, 2011,115, 6181-61897.
2. L. Tang, H.Chang, Y. Liu, J. Li. Adv. Funct. Mater, 2012, 22, 3083-3088.
3. S.Kundu, R. Dutta, A. Pyne and N. Sarkar. J. Phys. Chem. C, 2018,122, 6876-6888.
0.0
0.7
-1 0 1 40 500.0
0.7
0.0
0.7
0.0
0.7
No
rm
alize
d C
ou
nts
Delay Time (ps)
0 2 4 6 8 10 12
0.1
0.2
0.3
0.4
Time (ns)
48 g/ml
0 g/ml GO
r (t
)
10 100 1000 10000 1000000.0
0.4
0.8
1.2 0 g/ml GO
10 g/ml GO
20 g/ml GO
40 g/ml GO
50 g/ml GO
60 g/ml GO
70 g/ml GO
G(
)
Time (s)10 1000 100000
0.0
0.4
0.8
0 g/ml GO
10 g/ml GO
20 g/ml GO
40 g/ml GO
70 g/ml GO
G(
)
Time (s)
Static Quenching
Electron Transfer
52
Room Temperature Exciton and Trion Formation in Monolayer MoS2
Followed by Dissociation in Presence of Au NPs
Tanmay Goswami,a Renu Rani,a Kiran Shankar Hazra,b Hirendra N. Ghosh*,c
a PhD student, Institute of Nano Science & Technology, Habitat Centre, Sector 64, Mohali, Punjab
b Faculty, Institute of Nano Science & Technology, Habitat Centre, Sector 64, Mohali, Punjab
c Professor, INST, Mohali, Punjab; On deputation from Bhabha Atomic Research
Centre(BARC), Mumbai
Email ID: tanmay.ph17208@inst.ac.in
2D transition metal dichalcogenides have gained incredible interest and importance in
recent times, owing to their unique tunable optical, electronic and mechanical behaviours.
Reduced dielectric constant in 2D system, results in strong interactions between
quasiparticles, allowing formation of several stable many body states like excitons1, bi-
excitons2, and trions3 even at room temperature. Photophysical properties of 2D materials
are dominated by the behaviour of these quasiparticles and they are instrumental for various
applications of those materials. Here, we have studied carrier dynamics of monolayer MoS2
deposited on SiO2/Si substrate, before and after Au NP deposition, using broad band
femtosecond transient absorption spectroscopy4. Presence of both exciton and trion was
confirmed from steady state Photo-Luminescence (PL) measurements. MoS2 PL was
drastically quenched after deposition of Au NPs, indicating photo-excited electron transfer
from MoS2 to Au. From ultrafast spectroscopy we have calculated that, free carriers
generated from high energy pump excitations, turn into excitons within a time scale of
~500 fs and eventually form trions within ~1.2 ps. Excitons and trions are quickly
dissociated in presence of Au, with time scale of ~ 600 fs and ~3.7 ps respectively.
Fig: (a) TA spectra of monolayer MoS2; (b) TA kinetics of exciton A, exciton B and trion
A-; and (c) Comparative TA kinetics of pristine MoS2 and Au/MoS2 heterojunctions.
REFERENCES
(1) Scheuschner, N.; Ochedowski, O.; Kaulitz, A.-M.; Gillen, R.; Schleberger, M.;
Maultzsch, J. Phys. Rev. B 2014, 89, 125406. (2) Sie, E. J.; Frenzel, A. J.; Lee, Y.; Kong,
J.; Gedik, N. Phys. Rev. B 2015, 92, 125417. (3) Heinz, T. F.; Mak, K. F.; He, K.; Lee,
C.; Shan, J.; Hone, J.; Lee, G. H. Nat. Mater. 2012, 12, 207–211. (4) Goswami, T.; Rani,
R.; Hazra, K. S.; Ghosh, H. N. J. Phys. Chem. Lett. 2019, 10, 11, 3057.
53
Ultrafast carrier dynamics of Cu doped CdSe nanotetrapods
Fariyad Ali,a Sucheta Banerjee,a Anindya Datta.ab
a Department of chemistry, IIT Bombay, Powai, Mumbai, 400076 b Faculty, Department of Chemistry, IIT Bombay, adutta@iitb.ac.in
It is important to know the carrier relaxation in excited state of Cu doped CdSe
nanotetrapods (NTPs) as it has many applications in in different fields like LEDs,
photovoltaic devices, solar cells and transisters etc.1,2 We have studied the optical
properties and exciton dynamics after Cu doping in CdSe TPs in excited state. The PLQYs
of CdSe TPs increased from 1.42% to 9,8% after Cu doping and the PL decay time also
increased because conduction band electron recombine to the Cu2+ (d-level) hole instead
of direct electron-hole recombination.3,4 We have performed Transient Absorption (TA)
Spectroscopy to know the hot electron cooling time and recovery kinetics of exciton at
different pump power in excited state. It is observed that the hot electron relaxation time
increased from 580fs to 720fs and recovery kinetics also slowed after Cu doping in CdSe
TPs. So slow electron and recovery kinetics is depends on dopant concentration.5
REFERENCES
1. Zou, H.; Liu, M.; Zhou, D.; Zhang, X.; Liu, Y.; Yang, B.; Zhang, H. J. Phys. Chem.
C 2017, 121, 5313−5323.
2. Archer, P. I.; Santangelo, S. A.; Gamelin, D. R, Nano Lett. 2007, 7, 1037−1043.
3. Viswanatha, R.; Brovelli, S.; Pandey, A.; Crooker, S. A.; Klimov,V. I, Nano Lett.
2011, 11, 4753−4758.
4. Brovelli, S.; Galland, C.; Viswanatha, R.; Klimov, V. I, Nano Lett. 2012, 12,
4372−4379.
5. Dutta, A.; Bera, R.; Ghosh, A.; Patra, A, J. Phys. Chem. C 2018, 122 (29), 16992–
17000.
54
Ultrafast all-optical detection of interfacial spin transparency for pure spin current
transport in CoFeB/β-Ta thin films
Surya Narayan Panda1, Sucheta Mondal1, Samiran Choudhury1, Jaivardhan Sinha1, 2 and
Anjan Barman1,* 1Department of Condensed Matter Physics and Material Sciences, S. N. Bose National
Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata -700 106, India 2Department of Physics and Nanotechnology, SRM Institute of Science and Technology,
Kattankulathur-603203, Tamil Nadu, India
*Email address: abarman@bose.res.in
Spin pumping effect is an efficient mechanism for generating pure spin current, which is
the backbone of energy efficient new generation spintronic devices. Here we have
investigated the spin pumping effect [1] in sputter deposited β-Ta/CoFeB bilayer thin films
by measuring its imprint on Gilbert damping using all-optical femtosecond time-resolved
magneto-optical Kerr effect (TR-MOKE) technique. Thickness of Ta (t) and CoFeB (d)
have been varied from 1.0 to 20.0 nm and 1.0 to 13.0 nm, respectively, during the
experiment. The alternative interfacial effects on transport of pure spin current is also
investigated by introducing a Cu dusting layer of varying thickness, c (0.4 ≤ c ≤ 1.0 nm)
in-between the Ta and CoFeB layers. The precessional magnetization dynamics is
measured by using optical pump-probe technique with 10 mJ/cm2 pump pulse (λ = 400 nm,
pulse width = 50 fs) and 2 mJ/cm2 probe pulse (λ = 800 nm, pulse width = 40 fs) under a
constant in-plane bias magnetic field [2]. By analyzing the time-resolved Kerr rotation,
effective damping (αeff) parameter is extracted [fig. 1(a)]. The non-monotonic variation of
αeff with Ta thickness is modeled using spin pumping formalism to extract the spin
diffusion length of β-Ta as 2.44 ± 0.1 nm (fig. 1(b)) and its intrinsic spin-mixing
conductance as 7.22±0.05×1014 cm-2. The effective spin-mixing conductance is found to
be: 6.92±0.04×1014 cm-2 from the variation of αeff with the thickness of CoFeB layer (fig.
1 (c)). From these, we have obtained the interfacial spin transparency (T) of β-Ta/CoFeB
as 0.50 ± 0.03 by using the spin-Hall magnetoresistance effect model [3], which has direct
correlation with the effective spin-mixing conductance [4]. We have further inserted a Cu
dusting layer of varying thickness c between the β-Ta and CoFeB layer to eliminate the
other possible interface effects in the variation of damping such as interfacial hybridization,
two-magnon scattering, spin memory loss and Rashba effect. Invariance of αeff with Cu
layer thickness rationalizes our interface spin transparency argument in support of
electronic band matching and confirms the role of spin transparency in generation of pure
spin current by spin pumping effect.
We acknowledge financial support from S. N. Bose National Centre for Basic Sciences
(grant no.: SNB/AB/18-19/211). SNP and SC acknowledge S. N. Bose National Centre for
Basic Sciences, while SM acknowledge DST-INSPIRE scheme for respective research
fellowships.
REFERENCES [1] Y. Tserkovnyak, A. Brataas, G. E. W. Bauer, Phys. Rev. Lett. 88,117601 (2002).
[2] A. Barman and J. Sinha, Spin Dynamics and Damping in Ferromagnetic Thin Films and
Nanostructures, Springer, 2018, DOI: 10.1007/978-3-319-66296-1.
[3] W. F. Zhang, W. Han, X. Jiang, S. H. Yang, S. S. P. Parkin, Role of transparency of in determining
the intrinsic magnitude of the spin Hall effect. Nat. Phys. 11, 496 (2015).
[4] S. N. Panda, S. Mondal, J. Sinha, S. Choudhury, A. Barman, All-optical detection of interfacial spin
transparency from spin pumping in β-Ta/CoFeB thin films. Sci. Adv. 5, eaav7200 (2019).
55
Synthesis and Carrier Dynamics of Highly Luminescent Violet- and Blue-Emitting
Perovskite Nanocrystals
Apurba De, Somnath Das, Navendu Mondal and Anunay Samantaa aSchool of Chemistry, University of Hyderabad, Hyderabad- 500046, India,
Email: anunay@uohyd.ac.in.
Among the lead halide perovskites, photoluminescence quantum yield (PLQY) of violet-
emitting CsPbCl3 nanocrystals (NCs) is the lowest (<5%), which is an impediment to the
development of perovskite-based materials for optoelectronic applications covering the
entire visible region.1 While PLQY of the green- and red-emitting perovskites of this class
has been raised to near-unity, achieving a similar level for violet- and blue-emitting NCs is
still quite challenging.2,3 We report a novel method of simultaneously passivating the
surface defects and crystal disorder of violet-emitting CsPbCl3 NCs to dramatically
enhance (by a factor of∼120) the PLQY and stability without affecting the peak wavelength
(403 nm) and full-width at half-maximum (FWHM) of the photoluminescence (PL) band.4
We show that the addition of the correct quantity of CuCl2 during the hot-injection
synthesis of CsPbCl3 NCs leads to doping of Cu+ into the NCs, which rectifies octahedral
distortion of the crystal and the Cl- passivates the surface; the combined influence of the
two results in huge PL enhancement.4 NCs emitting throughout the blue region (430-460
nm) with near-unity PLQY (92%-98%) can then be obtained by partial halide-exchange of
the doped sample. Femtosecond transient absorption studies have been carried to
investigate the intrinsic photophysics and it suggest major suppression of the ultrafast
carrier trapping process in the doped NCs. The results might help in extending the utility
of these materials in optical applications by covering the entire violet−blue region.
REFERENCES
1. L. Protesescu,S. Yakunin,M. I. Bodnarchuk, F. Krieg, R. Caputo, C. H. Hendon, R. X. Yang, A.
Walsh and M. V. Kovalenko, Nano Lett. 2015, 15, 3692.
2. S. Seth, T. Ahmed, A. De and A. Samanta, ACS Energy Lett. 2019, 4, 1610.
3. N. Mondal, A. De and A. Samanta, ACS Energy Lett. 2019, 4, 32.
4. A.De, S. Das, N. Mondal and A. Samanta, ACS Materials Lett. 2019, 1, 116.
56
Facets of Carbon Nanodot: Fundamentals and Applications
Debashis Panda,a Surja Kanta Pal, Farogh Abbas, Shibam Saha a Rajiv Gandhi Institute of Petroleum Technology, An Institute of National Importance, Uttar Pradesh
dpanda@rgipt.ac.in
The synthetic origin of nanodimension and its role on the luminescence properties
of carbon nanodots, in particular, citric acid derived ones, remain an enigma to date.1 We
have identified that the citrazinic acid alone builds a nanocarbon structure upon incubation
in dimethyl formamide at room temperature. The emission properties of incubated
fluorophore resemble that of a nanodot. The dispersion of the H-bonded cluster’s size
originated from citrazinic acid only is the cause of excitation-dependent emission. We have
shown that the steric hindrance caused by the presence of alkyl chain of butyl amine
restricts such dispersions, resulting in excitation-independent emission, a molecular
behavior.1
We have made attempt to undersatnd the photoluminescence dynamics of so-called
doped nanodot in solid polymer matrix and that even in the presence of silver nanoparticle.
Surprisingly, it has been observed that the nanodot exhibits anomalous behavior metallic
nanoparticle. We also identify the existence of blue-, green-, and red-emissive fluorophores
in a product obtained from solvothermal reaction. The red luminescence has been used for
logic-gate operation for achiving molecule-on-a-Chip. Nanodot-embedded PVA/PVP film
has been used for down energy convesrsion to White Light using GaN UV-LED Chip.2
The mechanism of white light emission is attributed to effective energy transfer among
fluorophores.4
REFERENCES
1. Kaleem, W.; Kumar, A.; Panda, D. J. Phys. Chem. C 2018, 122, 26722.
2. Nandy, A.; Kumar, A.; Dwivedi, S.; Pal, S.K.; Panda, D. J. Phys. Chem. C 2019, 123, 20502.
Abbas, F.; Kumar, S.; Panda, D. (Communicated, 2019)
57
Ultrafast photoinduced electron transfer dynamics between cyclometalated rhodium
and iridium complexes and cyan emitting copper nanoclusters
Soumyadip Bhunia, Pradipta Purkayastha
Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Kolkata,
Mohanpur 741246, WB, India, ppurkayastha@iiserkol.ac.in
In recent times, copper nanoclusters (Cu NCs) have become promising as
interesting nanomaterials for their potential applications in optoelectronics, sensing,
catalysis and bioimaging.1 Herein, we have synthesized L–Cysteine protected Cu NC in
1:1 water:acetonitrile (ACN) solvent possessing bright cyan emission (λem=495 nm) with
10.4% fluorescence quantum yield.2 Furthermore, the cyclometalated complexes of Ir(III)
and Rh(III) are light harvesters and applied in photoinduced electron and energy transfer
and photocatalysis. Three such cyclometalated complexes of Rh and Ir have been used over
here,3 which on electrostatic interaction with Cu NCs in 1:1 water:ACN medium,
dramatically quench the fluorescence of the Cu NCs. This quenching could be suitably
attributed to photoinduced electron transfer (PET) where the Cu NCs act as electron
acceptor. PET was confirmed by steady state and time resolved fluorescence spectroscopy
as well as by ultrafast femtosecond upconversion and transient absorption spectroscopy.
We have studied the dynamics of PET using the ultrafast spectroscopic techniques to
provide an elaborate description of the phenomenon. The present studies, thus, provide a
new pathway in light harvesting research and expected to be applicable in creating energy
devices.
Figure 1. Photoinduced electron transfer from Cyclometalated complexes to Cu NC.
REFERENCES
1. S. Kundu, A. Patra, Chem. Rev. 2017, 117, 712.
2. S. Bhunia, S. K. Seth, P. Gupta, M. Karmakar, P. K. Datta, P. Purkayastha, Chemistry Select 2019, 4,
8568.
3. S. K. Seth, P. Gupta, P. Purkayastha, New J. Chem. 2017, 41, 6540.
58
Determination of dispersion of the third order optical nonlinearity of Carbon
Dots
T. Singha1, M Bera2, S. Bhattacharya1,3, N.D. Pradip Singh2, P.K. Datta1
1Department of Physics, Indian Institute of Technology Kharagapur, Kharagpur, India 721302 2Department of Chemistry, Indian Institute of Technology Kharagapur, Kharagpur, India 721302 3currently at Department of Chemistry, University of Sheffield, Sheffield S3 7HF, United Kigdom
Excellent tunable fluorescence properties of carbon dots (C-dots) facilitate diverse
biological applications owing to their stability, good biocompatibility and low toxicity.1 C-
dots are zero dimensional, spherical shaped nanoparticles with diameter less than 10nm,
composed of non-toxic C, O and N elements. C-dots consist of two parts, carbon core and
surface functional groups (-OH, -COOH, -NH2, etc). In the carbon core, carbon atoms form
sp2 hybridized C=C bonds and the surface functional groups form sp3 hybridized bonds.2
The band gaps vary with their sizes which is promising for tunable nonlinear optical
phenomena. Panagiostis et al. had studied the sizable nonlinear absorption and the negative
nonlinear refraction of C-dots in ns regime.3
The microwave synthesized carbon dots are spherical in shape with particle sizes ~3nm.
The UV-Visible absorption spectrum shows that carbon dots exhibiting the first band-gap
(Eg1) at ~5.17 eV and second band-gap (Eg2) at ~3.65 eV. We have studied the dispersion
of third order nonlinearity (n2) 4,5 of C-dots using single beam Z-Scan technique6 with
different photon energies. Since carbon dots behave as semiconductors7, they show
dispersion property of n2. The measurements were taken by laser pulses (pulse width
~100fs) at wavelength range varying from 480nm (2.58eV) to 600nm (2.06eV) (in 20nm
wavelength spacing). It has been found that the n2 values are negative above the first and
second half band gap (Eg1/2=2.58eV, Eg2/2=1.82eV) and are positive below first half band
gap (Eg1/2=2.58eV) of carbon dots. This study highlights the tunable nonlinear optical
properties of C-dots which have potential for many optical devices like optical limiters,
optical switches, etc.
REFERENCES:
1. Ju Wang, J. Mater. Chem. A, 2017, 5, 3717
2. Namasivayam Dhenadhayalan, J. Phys. Chem. C 2016, 120, 1252−1261
3. Panagiostis Aloukos, Optics Express 12013, 22, 10, 2014
4. M. Sheik-Bahae. PRL, vol. 65, no. 1, July 1990
5. Ningning Dong, Optics Letters, 3936, 41, 14, 2016
6. M. Sheik-Bahae. IEEE Journal of Quantum Electronics. vol. 26. no. 4, April 1990
Monoj Kumar Barman, J. Phys. Chem. C 2014, 118, 20034−20041
59
INVESTIGATION OF IMPROVED CHARGE CARRIER DYNAMICS OF
CORE-SHELL NANOCRYSTAL MODIFIED PEROVSKITE USING
TRANSIENT ABSORPTION SPECTROSCOPY
Sayan Prodhan1#, Kamlesh Kumar Chauhan2, Anima Ghosh3, Sayan Bhattacharaya3,
Prasanta Kumar Datta1*
1Department of Physics, Indian Institute of Technology (IIT) Kharagpur, Kharagpur – 721302, India 2Department of Electrical Engineering, Indian Institute of Technology (IIT) Kharagpur, Kharagpur –
721302, India 3Department of Chemical Sciences, and Centre for Advanced Functional Materials, Indian Institute of
Science Education and Research (IISER) Kolkata, Mohanpur 741246, India
*E-mail address: sayan.prodhan@gmail.com
Recent discoveries of highly efficient solar cells based on organic-inorganic lead
halide perovskites attract a surge in research activity. Its improvement in solar cell
efficiency from 10% to 25.2% in just one decade has shown its very promising future as
solar cell. The reason behind its amazing performance is its high absorption coefficient;
high PLQY, high charge carrier mobility, long diffusion length, and low trap state density
that affects the performance of perovskite based solar cell. We have modified MAPbI3-
XClX perovskite using Au/CZTS core/shell nanocrystal (NC) and it improves the solar cell
efficiency from 12.83% to 19.97%. Understanding the photo-carrier dynamics and
interactions are crucial for elucidating the working mechanisms and improvement
pathways of mixed halide perovskite based solar cells. Transient absorption spectroscopy
has been performed on both unmodified and modified mixed halide perovskite to
investigate its photo-carrier dynamics. We have used 480 nm (2.58 ev) as pump at a fluence
of ≈ 12.5 μJ/cm2 which is way above its band-gap and white light (350nm-850nm) as
probe. The transient absorption spectra shows increased bleaching magnitude and
increased bleaching bandwidth after the nano-crystal modification. Increase in bleaching
magnitude is the result of the increased absorption coefficient due to the plasmonic effect
of the Au/CZTS core/shell NC. Decay kinetic study of the photo-bleaching signal for both
unmodified and modified MAPbI3-XClX perovskite is performed with the help of tri-
exponential function and various phenomenon like hot carrier cooling, trap state
recombination and auger recombination has been correlated with the decay time constants.
After modification, the hot carrier cooling time is increased from 0.3ps to 6.45 ps indicating
hot phonon bottleneck effect1,2 due to the increase in number of excited carriers. High
number of excited carrier suppress the decay of LO phonon to LA phonon and results in
60
reheating of the excited carriers. Passivation effect3,4 of Au/CZTS core/shell NC decreases
the trap state density as it smoothen the surface. It increases trap state recombination time
from 48.3ps to 850 ps. Also the core-shell configuration5,6 induces spatial separation
between those participating electron and hole that hinders the auger recombination. This
increases the auger recombination time from 452ps to 8212ps. The combined effect of
increase in the absorption coefficient and the elongation in the charge carrier lifetime due
to the modification improves the overall efficiency of the perovskite solar cell.
REFERENCES 1. Ye Yang, David P. Ostrowski, Ryan M. France, Kai Zhu, Jao van de Lagemaat, Joseph M. Luther
and Matthew C. Beard. Observation of a hot-phonon bottleneck in lead-iodide perovskites. Nature
Photonics 2016, 10, 53–59
2. M. B. Price, J. Butkus, T. C. Jellicoe, A. Sadhanala, A. Briane, J. E. Halpert, K. Broch, J. M.
Hodgkiss, R. H. Friend, and F. Deschler, "Hot-carrier cooling and photoinduced refractive index
changes in organic–inorganic lead halide perovskites," Nat. Commun. 6, 8420 (2015).
3. Qi Jiang , Zema Chu, Pengyang Wang, Xiaolei Yang, Heng Liu, Ye Wang Zhigang, Yin Jinliang
Wu, Xingwang Zhang and Jingbi You. Planar-Structure Perovskite Solar Cells with Efficiency
beyond 21%. Adv. Mater. 2017, 29, 46
4. Dae-Yong Son, Jin-Wook Lee, Yung Ji Choi, In-Hyuk Jang, Seonhee Lee, Pil J. Yoo, Hyunjung
Shin, Namyoung Ahn, Mansoo Choi, Dongho Kim and Nam-Gyu Park. Self-formed grain boundary
healing layer for highly efficient CH3 NH3 PbI3 perovskite solar cells. Nature Energy 2016, 1,
16081
5. Young-Shin Park, Wan Ki Bae, Lazaro A. Padilha, Jeffrey M. Pietryga and Victor I. Klimov. Effect
of the Core/Shell Interface on Auger Recombination Evaluated by Single-Quantum-Dot
Spectroscopy. Nano Lett.2014,14 , 396-402
6. Florencio García-SantamaríaYongfen, ChenJavier, VelaRichard D. SchallerJennifer A.
Hollingsworth and Victor I. Klimov. Suppressed Auger Recombination in “Giant” Nanocrystals
Boosts Optical Gain Performance. Nano Lett.2009,9, 10, 3482-3488
61
Study of Non-colinear Femtosecond Second Harmonic and Sum Frequency
Generation using BBO crystals. aSushanta Lenka, aSailab Singh Bodra,b Kamlesh Kumar Chauhan, Prasanta Kumar Datta
a,b aDepartment of Physics, IIT Kharagpur, West Bengal, , India – 721302.
bDepartment of Electrical, Engineering IIT Kharagpur, West Bengal, India – 721302.
For generating second harmonic generation (SHG) and sum frequency
generation (SFG) in femtosecond regime, mostly we have to keep in mind
about the following three parameters. (1) Special overlap, (2) Zero delay, (3)
Phase matching. We have used fiber based femtosecond laser pulses of
repetation rate 80MHz (Average Output power > 100mW). First,we have
generated non collinear SHG of two input femtosecond pulses (780nm) using
BBO crystal of thickness 3mm and cut axis 26 degree. Secondly, we have
generated non collinear SFG of two different input femtosecond pulses
(780nm and 1560nm) using BBO crystal of thickness 6mm and 0.5mm. For
type- 1 interaction , we have fixed two input pulses are ordinary polarized (o
& o-polarized). The input power pulses are maintained as 32mW and the
spectral band width is around 17nm as observed using Avantage spectrometer
.The powers of generated SHG pulses are measured around 0.62mW with the
spectral bandwidth of 4 nm.The high quality image of generated SHG signal
is captured by high resolution camera. The generated SHG power is 0.42mW
with spectral bandwidth of 6nm. Both theritical and experimental
investigation we have performed.
The narrow spectral width of SFG pulse is obtained from the result. It
is due to the relation that the spectral bandwidth is inversely proportional to
crystal thickness. The spectral band width can be enhance by compromising
the thickness of the BBO crystal. The power conversion efficiency of
generated SHG is around 1.5 %. The conversion efficiency we have improved
by controling the phase matching angle by changing external angle between
two input femtosecond pulses and thickeness of BBO crystal.
REFERENCES
1. Andrew J. W Brown, Mark S. Bowers, Ken W Kangas, and Charles H. Fishers
OPTICS LETTERS.
2. O. Gobert,1 G. Mennerat,1 R. Maksimenka,1,2 N. Fedorov,1 M. Perdrix,1D.
Guillaumet,1 C. Ramond,3,4 J. Habib,3,4,5,6 C. Prigent,3,4 D. Vernhet,3,4 T.
Oksenhendler,2 and M. Comte1, APPLIED OPTICS.
62
Solvent Mediated Relaxation Dynamics of Core-Shell Au-SiO2 Nanoparticles
Hemen Gogoi,a Bala Gopal Maddala,b Anindya Dattaa a Department of Chemistry, Indian Institute of Technology Bombay
bIITB-Monash Research Academy
Mumbai, Maharashtra-400076
The inherent plasmonic property of nanosized gold particles makes it useful for various
applications ranging from photovoltaics to photothermal therapy.1 The crucial heat
dissipation dynamics of these nanostructures can be effectively probed with the help of
transient absorption spectroscopy. This technique helps us to understand the different
pathways involved in the relaxation dynamics of excited Au-SiO2 core-shell
nanoparticles.2 Initially gold nanoparticles are synthesized by reducing the gold precursor
and then coated with silica by using tetraethyl orthosilicate (TEOS) to enhance its stability.3
Synthesized nanoparticles were dispersed in solvents with different thermal conductivities.
By exciting the solutions with a strong laser pulse, the evolution of the excited state
dynamics in different surrounding environment has been monitored. The electron-phonon
relaxation time of Au-SiO2 nanoparticles has been found to be increased with decrease in
thermal conductivity of the solvent while the phonon-phonon relaxation time remains
unaffected.
REFERENCES
1. Carattino, A.; Caldarola, M.; Orrit, M. Nano Lett. 2018, 18, 874.
2. Mohamed, M. B.; Ahmadi, T. S.; Link, S.; Braun, M.; El-Sayed, M. A. Chem. Phys.
Lett. 2001, 343, 55.
3. Fernández-López, C.; Mateo-Mateo, C.; Álvarez-Puebla, R. A.; Pérez-Juste, J.;
Pastoriza-Santos, I.; Liz-Marzán, L. M. Langmuir 2009, 25, 13894.
63
Ultrafast dynamics of gold dimers and trimers
Bala Gopal M,abc Alison Funston,ab Anindya Dattaac (a) IITB-Monash Research Academy, Mumbai, India (b) School of chemistry, Monash University, Melbourne, Australia
(c) Department of chemistry, IIT Bombay, Mumbai, India
Ultrafast dynamics of nanoparticles have garnered much attention in the past decade due to their optical
nonlinear properties.1-3 In the present study, the excited state electron relaxation dynamics of gold dimers and
trimers were studied employing femtosecond laser pump probe spectroscopy. Controlled assemblies of gold
nanospheres such as gold dimers and trimers were prepared using a dithiol linker molecule.4 Different optical
response was observed in dimer and trimers as compared to monomers in solution phase. Global fit analysis
was employed to understand the relaxation dynamics and we compared the results with conventional kinetic
fit analysis underlying its disadvantages in assembled systems where there is huge spectral overlap of positive
and negative signals in the red shifted plasmon coupling region. Our results suggest that enhanced electron-
phonon and phonon-phonon coupling time in higher assemblies as compared to monomers. This is attributed
to higher spectral overlap of electron oscillation and phonon spectrum in the region of enhanced electric field
intensity.2,5
Figure 1. Gold nanoparticle assemblies
Figure 2. Pseudo color heat map of Transient absorption spectra of a) gold NP monomers b) Dimers c)
Trimers
References
1. Xia, Y.; Xiong, Y.; Lim, B.; Skrabalak, S. E. Angew. Chemie Int. Ed. 2009, 48 (1), 60.
2. Link, S.; El-Sayed, M. A. Annu. Rev. Phys. Chem. 2003, 54 (1), 331.
3. Kelly, K. L.; Coronado, E.; Zhao, L. L.; Schatz, G. C. J. Phys. Chem. B 2003, 107 (3),668.
4. Bidault, S.; Polman, A. Int. J. Opt. 2012, 2012.
5. Fernández-López, C.; Mateo-Mateo, C.; Álvarez-Puebla, R. A.; Pérez-Juste, J.;Pastoriza-
Santos, I.; Liz-Marzán, L. M. Langmuir 2009, 25 (24), 13894.16
64
Slow Charge Carrier cooling in Type-1 3D/0D Core-Shell CsPbBr3@Cs4PbBr6
Perovskite system: Role of Polaron Formation
Gurpreet Kaur a, K. Justice Babu b and Hirendra N. Ghosh c
a PhD student, Institute of Nanoscience and Technology (INST), Habitat Center, Sector 64, Mohali
b Post Doctoral Fellow, Institute of Nanoscience and Technology (INST), Habitat Center, Sector 64, Mohali
c Professor, INST, Mohali, Punjab; On deputation from Bhabha Atomic Research
Centre(BARC),Mumbai
a Email id: gurpreet.ph17205@inst.ac.in
Fast hot carrier cooling is the key parameter surpassing all the other possible energy loss
pathways, which are broadly encountered in every other single junction solar cell, hence
setting a thermo-dynamical bar on the achievable solar energy conversion
efficiency(Shockley Quiesser limit~33%).1 Thus, retardation of hot carrier cooling rate in
the cell absorber layer can make hot carrier extraction a less cumbersome task ,making
the realization of hot carrier solar cell practical(boosting the solar cell performance
beyond 67%).2 Recently, there have been plentitude of reports concerning the slow carrier
cooling in lead halide perovskite materials, which eventually triggered growing interest in
the radical understanding of the native photophysics playing an important role in the
device design3. Here in this finding, a further dramatic dip in the cooling rate has been
discerned upon growing a Cs4PbBr6 shell over CsPbBr3 core NCs in crude contrast to the
bare CsPbBr3core NCs. Using the broadband ultrafast Transient Absorption (TA)
spectroscopy, we have investigated the disparity in the thermalisation pathways taken up
by the hot carriers in the CsPbBr3 and CsPbBr3@Cs4PbBr6 core-shell NC systems under
same incident laser fluence, which can be validated as a corollary of large polaron
formation taking place in the later NC systems. There are clear evidences of polaron
formation in the femtosecond TA data of the core-shell system which is much suppressed
in case of CsPbBr3.This knowledge can be steered to drive towards the achievement of
higher Voc,which is a commanding factor detrimental for the efficiency of the solar cell.
References
1. Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.;
Walsh, A.; Kovalenko, M. V. Nano Lett. 2015, 15 (6), 3692–3696.
2. Manser, J. S.; Kamat, P. V. Nat. Photonics 2014, 8, 737.
3. Kaur, G.; Babu, K. J.; Ghorai, N.; Goswami, T.; Maiti, S.; Ghosh, H.N.; J. Phys. Chem. Lett., 2019,
10, 5302.
65
Long-Range Resonance Coupling-Induced Surface Energy Transfer
from CdTe Quantum Dot to Plasmonic Nanoparticle
Jamuna K. Vaishnav and Tushar Kanti Mukherjeea aDiscipline of Chemistry, Indian Institute of Technology Indore, Simrol, Indore
E-mail: tusharm@iiti.ac.in
Fundamental understanding and precise control of complex nonradiative processes in
nanoscale system finds significant interest in recent times due to their importance in various
nanophotonics applications. Here we have systematically investigated the mechanism
behind photoluminescence (PL) quenching of mercaptosuccinic acid (MSA) capped CdTe
QDs in the near field of gold and silver nanoparticles (Au and Ag NPs) by using steady-
state and time-resolved photoluminescence (PL)spectroscopy. Resonance coupling
between excitonic emission and localized surface plasmon resonance (LSPR) of Au NPs
has been tuned by varying the size of QDs.
Herein, three differently sized MSA-capped CdTe QDs have been synthesized
namely,2.1 ± 0.7, 3.1 ± 0.4, and 3.9 ± 0.3 nm with emission in green, yellow and red region
of the electromagnetic spectrum, respectively. It has been observed that both the
luminescence intensity and lifetime of green QDs quench significantly in the near field of
20 nm sized Au NPs. In contrast, the luminescent intensity and lifetime of yellow and red
QDs remain unaltered in the presence of Au NPs. Moreover, it has been observed that
ligand exchange at the surface of Au NPs with Poly(ethylene glycol) methyl ether thiol
(PEG-SH) decreases the quenching efficiency of the green QD-Au NP pair significantly.
In addition, the extent of quenching strongly depends on excitation wavelength. The
observed quenching is more efficient at the excitation wavelength close to the LSPR of Au
NP. These results have been explained on the basis of a size-dependent nanometal surface
energy transfer (NSET) model by incorporating the changes in the complex dielectric
function and the absorptivity of the Au NP. On the contrary, irrespective of the sizes of
QDs,significant PL quenching has been observed in the presence of 10 nm sized citrate-
capped Ag NPs as a consequence of photoinduced electron transfer (PET). The present
findings of size and wavelength-dependent long-range nonradiative electromagnetic
coupling in hybrid QD-metal NP system can be useful to understand and optimize the
performance of various nanophotonic devices.
REFERENCES
1. J. K. Vaishnav, T. K. Mukherjee, J. Phys. Chem. C 2018, 122, 28324-28336.
66
Time Dependent Optical Second Harmonic Generation from Si/SiO2 Interface and
Its Variation with Doping Concentration
Binit Mallicka, Anindya Duttab, Swaroop Gangulyc a Department of Electrical Engineering, IITB
b Department of Chemistry, IITB, anindya@chem.iitb.ac.in
c Department of Electrical Engineering, IITB, sganguly@ee.iitb.ac.in
We have investigated a nondestructive and contactless characterisation technique
using time dependent optical second harmonic generation (TDSHG). The TDSHG method
is used to probe electron trapping phenomena on silicon dioxide surface from silicon
(Si)/silicon dioxide (SiO2) interface. A phenomenological explanation is provided for the
time dependent second harmonic (TDSH) intensity. We have studied the relationship
between SH intensity and its time dependent behaviour with varying doping concentration
and oxide thickness. We have also studied the rotational asymmetrical nature of SH
intensity from Si/SiO2 interface. An explanation is provided for the observed trend.
REFERENCES
1. J. G. Mihaychuk, J. Bloch, Y. Lui, and H. M. van Driel, Opt. Lett. 20, 2063 (1995).
2. J. Bloch, J. Mihaychuk, H. M. van Driel, Phys. Rev. Lett. 77, 920 (1996).
3. J. I. Dadap, X. F. Hu, M. H. Anderson, M. C. Downer, J. K. Lowell, and O. A. Aktsipetrov, Phys.
Rev. B 53, R7607(R),(1996).
4. J. G. Mihaychuk, N. Shamir, and H. M. van Driel, Phys. Rev. B 59, 2164, (1999)
Julie L. Fiore, Vasiliy V. Femenko, Dora Bodlaki and Eric Borguet , Appl. Phys. Lett. 98, 041905 (2011).
67
Direct Observation of -Phonon Driven Ultrafast Magnetization Dynamics in
Ferromagnetic Nanodot Arrays
Arundhati Adhikari, Koustuv Dutta, Anulekha De and Anjan Barman*
Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic
Sciences, Block JD, Sector III, Salt Lake, Kolkata 700 106, India
*abarman@bose.res.in
Ultrafast dynamic response in ordered nanomagnet arrays1 has remained a field of immense
interest for researchers because of its huge potential application in the next generation
spintronic and magnonic devices. In recent years, researchers have explored various new
routes to enhance the functionality of magnonic crystals by manipulating the spin-wave
dynamics, by various external stimuli and coupling with various quasiparticles and a new
field of cavity magnonics has emerged2. In such ordered system, the coupling of magnons
with phonon, photon or another magnon is very interesting from the perspective of
fundamental understanding as well as novel devices. Here, we have investigated phonon
driven magnon dynamics in Permalloy (Ni80Fe20) nanodots of square shape arranged in
closely packed hexagonal symmetry in femto to nanosecond time scale. We have used a
custom-built time-resolved magneto-optical Kerr effect (TRMOKE) microscope where an
ultrashort laser pulse (80 fs) of wavelength 800 nm is used to probe the dynamics of both
the magnetic and non-magnetic origin after being excited by the second harmonic of this
laser of 400 nm wavelength. We observe prominent oscillation in the time-dependent
reflectivity signal that ensures the generation of elastic vibration (phonon) in the system,
which is strongly correlated with the array geometry3. The frequency spectra of the elastic
mode show multiple peaks in GHz frequency regime, which also overlaps with the magnon
modes in certain bias field regime. The bias field variation reveals the coupling between
the magnon and phonon modes from the observed crossing/anti-crossing between the two
modes. The magnon-phonon coupling is interpreted on the basis of existing analytical
theory. The observation of tunability of this strong magnon-phonon coupling with lattice
parameters would be important for the emerging field of cavity magnonics and
magphonics.
We gratefully acknowledge the financial support from S. N. Bose National Centre for Basic
Sciences (SNB/AB/18-19/211). AA acknowledges S. N. Bose Centre and KD and AD
acknowledge DST (INSPIRE Scheme) for research fellowship.
REFERENCES
1. B. Rana et al., ACS Nano, 2011, 9559, 5
2. Y. P Wang et al., Phys. Rev. Lett. 2018, 057202, 120
3. A. Comin et al., Phys. Rev. Lett. 2006, 217201, 97.
68
Comprehensive study of femtosecond transient carrier dynamics in mixed halide
perovskite
Kamlesh Kumar Chauhan, a Sayan Prodhan, b Sayan Bhattacharyya, c Pranab Kumar
Dutta, a Prasanta Kumar Datta b a Department of Electrical, Engineering IIT Kharagpur, West Bengal, India – 721302.
b Department of Physics, IIT Kharagpur, West Bengal, , India – 721302.
c Department of Chemical Science, IISER Kolkata, Mohanpur, West Bengal, India – 741246.
Organic-inorganic perovskite "a third generation photovoltaic" has completely
attracted the interest among photovoltaic research community. Its novel optical properties
like high absorption coefficient1, high carrier mobility2, large carrier diffusion length3,
slow hot carrier cooling4 etc. are responsible for attaining maximum power conversion
efficiency of 25.2%5. The detailed study of photo-excited carrier dynamics is capable in
describing the improved device properties. The present work experimentally demonstrates
the carrier density dependent bleaching dynamics in organic-inorganic mixed halide
(CH3NH3PbI3-XClX) perovskite using transient absorption spectroscopy. The mixed halide
perovskite is excited well above the band-gap (1.6 eV) using the femtosecond pump pulse
of 480 nm (2.58 eV) and a white light probe (350-850 nm) pulse is utilized to observe the
transient carrier dynamics by measuring the change in absorption (ΔA) of probe due to
pump excitation. The transient absorption (TA) spectra shows a broad negative ΔA band
over 600-780 nm peaks at 730 nm which corresponds to joint effect of ground state
bleaching and state filling due to free carriers. The decay of band-limited bleaching signal
is analyzed well and shows the linear variation within the excited carrier density of 1018-
1019 cm-3. The bleaching decay is sequential fitted with the rate equation given by
2 3
1 2 3( ) ( ) ( ) ( )d
n t k n t k n t k n tdt
, where k1- monomolecular, k2- bimolecular and k3- tri-
molecular decay rate constants. The fitted results give the radiative recombination rate (k2)
of 10-11 cm-3s-1 resulting in the maximum attainable diffusion length of ~10 µm in mixed
halide perovskite. Our finding shows the potential of mixed halide perovskite in thin film
solar cell application.
REFERENCES
1. M Green, A Baillie, H Smith, Nature Photonics, 2014, 8, 506–514.
2. Y. Chen, H. T. Yi, X. Wu, R. Haroldson, Y. N. Gartstein, Y. I. Rodionov, K. S. Tikhonov,A.
Zakhidov,X. -Y. Zhu , V. Podzorov, Nature Comm., 2016, 7, 12253.
3. Ponseca et al J. Am. Chem. Soc. 2014, 136, 145, 189-5192.
4. Yang et al, Nature Photonics, 2016, 10, 1, 53-59.
National renewable energy laboratory, “Efficiency chart,” 2019,
https://www.nrel.gov/pv/assets/pdfs/best-research-cell-efficiencies.20190703.pdf
69
Carrier Dynamics Measurement on MoS2 Monolayers Using Ultrafast Pump-Probe
Spectroscopy
D. P. Khatua1,2,a), Asha Singh1, Sabina Gurung1,2 and J. Jayabalan1,2
1Nano Science Laboratory, Materials Science Section, Raja Ramanna Centre for Advanced Technology,
Indore, India-452013. 2Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai, India - 400085.
a)Corresponding author: khatuadurgaprasad03@gmail.com
Extensive research on two-dimensional materials (2DM) is being carried out in recent time due to their
application in optoelectronic and valleytronic devices. Among 2DM, monolayers of Molybdenum Disulfide
(MoS2) has attracted lot of interest due to its stability, existence of direct band gap and its larger exciton
binding energy [1, 2]. For understanding the optical response of MoS2, it is necessary to examine carrier
dynamics at various excitation densities. We have measured the ultrafast optical response of two-dimensional
MoS2 monolayer flakes using femtosecond oscillator-amplifier-OPA system in standard pump-probe
transmission geometry (Fig.1) and pulse width at the sample place is about 140 fs. The pump and probe
wavelengths were 400 nm and 420 nm respectively. Figure 2 shows the time evolution of transient
transmission (T/T) measured at different pump fluences near 1.0 mJcm-2. With increasing pump fluence the
peak change in T/T reduces. Transient measurement with increasing pump fluence in the range of 0.1 to 0.5
mJcm-2 showed a saturation behavior [3]. In the present case the reduction in peak change in T/T is
attributed to increased carier-carrier scattering process which starts the relaxation of carriers at earlier times
at higher excitation densities. It will also be shown that the decay time of T/T reduces with increase in pump
fluence. Reduction in decay times at higher fluence can be attributed to auger recombination process and
capture of carriers by defect states [4].
Fig.1: Schematic of pump-probe setup used for transient absorption measurements. The pump beam was generated by frequency doubling in BBO and probe beam was 420 nm.
Fig.2: Transient transmission of MoS2 sample at different pump fluences (dots). The green line shows the best fit to the data with increasing absorption density and single-exponential decay.
REFERENCES
1. Singh, A., Tran, K., Kolarczik, M., Seifert, J., Wang, Y., Hao, K., Pleskot, D., Gabor, N.M.,
Helmrich, S., Owschimikow, N. and Woggon, U., Phys. Rev. Lett., 117, 257402 (2016).
2. Miró, P., Audiffred, M., and Heine, T., Chem. Soc. Rev., 43, 6537-6554 (2014).
3. Seo, M., Yamaguchi, H., Mohite, A. D., Boubanga-Tombet, S., Blancon, J. C., Najmaei, S., and
Prasankumar, R. P., Sci. Rep., 6, 21601 (2016).
4. Wang, H., Zhang, C., Rana, F., Nano lett., 15, 339-345 (2014).
70
Exploring the Dynamics of Excited Excitonic Rydberg Series in Layered MoS2
Manobina Karmakar1, Sayantan Bhattacharya1,2, Subhrajit Mukherjee3,4, Barun
Ghosh5, Rup Kumar Chowdhury1, Amit Agarwal5, Samit Kumar Ray1,6 and Prasanta
Kumar Datta1
1Department of Physics, Indian Institute of Technology Kharagpur, Kharagpur, India 721302. 2currently at Department of Chemistry, University of Sheffield, Sheffield S3 7HF, United Kingdom. 3Advanced Technology and Development Centre, Indian Institute of Technology Kharagpur, Kharagpur,
India 721302. 4currently at Technion - The Israel Institute of Technology, Haifa, Israel. 5Department of Physics, Indian Institute of Technology Kanpur, Kanpur, India 208916. 6S. N. Bose National Centre for Basic Sciences, Kolkata, India 700106.
While optoelectronic technology is inching towards excitonic devices, external control and
manipulation of these neutral quasiparticles is an essential step towards realizing potential
applications. In this regard, transition metal dichalcogenides (TMDC) are the leading
candidates owing to their strongly bound excitons and associated unique optical
properties1-5. In this work, we explore the ultrafast response of ground (1s) and first excited
(2s) state of excitons in a few-layered TMDC (MoS2) upon above-bandgap photo-
excitation. Apart from Pauli blocking effect in 1s excitons, we observe a dynamically-
enhanced absorption of the 2s state. This is caused by the reduction in dielectric
permittivity, which is triggered by reduced 1s-2s energy separation upon photo-excitation,
at the particular resonance. Further, we estimate the contributions of various Coulomb
screening effects that determine the dynamical resonance energy separation of the 1s and
2s states and therefore lead to the interesting phenomenon of enhanced absorption. While
many of the existing studies in excitonic systems fail to distinguish electronic and optical
bandgap renormalization and observe the resultant effect in optical (i.e. excitonic)
bandgap6, we could de-couple the dynamic contribution from free electronic and bound
electronic effects. Our study provides key understanding for bandgap engineering and
insight into how Coulomb interactions respond to external perturbations in a few-layered
TMDC.
REFERENCES:
1. Cunningham, P. D.; Hanbicki, A. T.; McCreary, K. M.; Jonker, B. T. Photoinduced Bandgap
Renormalization and Exciton Binding Energy Reduction in WS2. ACS Nano 2017, 11, 12601–12608.
2. Chernikov, A.; Berkelbach, T. C.; Hill, H. M.; Rigosi, A.; Li, Y.; Aslan, O. B.; Reichman, D. R.;
Hybertsen, M. S.; Heinz, T. F. Exciton Binding Energy and Nonhydrogenic Rydberg Series in Monolayer
WS2. Phys. Rev. Lett. 2014, 113, 076802.
3. Ugeda, M. M.; Bradley, A. J.; Shi, S.-F.; da Jornada, F. H.; Zhang, Y.; Qiu, D. Y.; Ruan, W.; Mo, S.-K.;
Hussain, Z.; Shen, Z.-X. et al. Giant bandgap renormalization and excitonic effects in a monolayer
transition metal dichalcogenide semiconductor. Nature Materials 2014, 13, 1091.
4. Shi, H.; Yan, R.; Bertolazzi, S.; Brivio, J.; Gao, B.; Kis, A.; Jena, D.; Xing, H. G.; Huang, L. Exciton
Dynamics in Suspended Monolayer and Few-Layer MoS2 2D Crystals. ACS Nano 2013, 7, 1072–1080.
5. Raja, A.; Chaves, A.; Yu, J.; Arefe, G.; Hill, H. M.; Rigosi, A. F.; Berkelbach, T. C.; Nagler, P.;
Schüller, C.; Korn, T. et al. Coulomb engineering of the bandgap and excitons in two-dimensional
materials. Nature Communications 2017, 8, 15251.
6. Pogna, E. A. A.; Marsili, M.; De Fazio, D.; Dal Conte, S.; Manzoni, C.; Sangalli, D.;
Yoon, D.; Lombardo, A.; Ferrari, A. C.; Marini, A. et al. Photo-Induced Bandgap Renormalization
Governs the Ultrafast Response of Single-Layer MoS2. ACS Nano 2016, 10,
1182–1188.
71
Comparative study of ultra-fast thermal strain evolution in Ge (111) sample induced
by fundamental and second harmonic pump pulse
R. Rathorea,b*, H. Singhala,b and J. A. Chakeraa,b aHomi Bhabha National Institute, Training school Complex, Anushaktinagar, Mumbai - 400094
bLaser Plasma Division, Raja Ramanna Centre for Advanced Technology, Indore 452 013
*Email: ranjana@rrcat.gov.in
The study of photo-induced thermal strain propagation in semiconductor material is
especially important as the change in thermal properties may influence the performance of the ultra-
fast semiconductor devices. Excitation of semiconductor sample with an ultra-short laser pulse of
photon energy more than the band gap of the semiconductor sample results in single photon
absorption of the laser in the sample. This leads to heating of the sample and eventually dilation of
the lattice. The effect of laser excitation with different wavelengths (photon energy) but similar
fluence on the sample may be different as they will have different absorption depths. In view of
this, we have studied the evolution of thermal strain in the sample by the excitation of fundamental
(800 nm) and second harmonic (SH, 400nm) laser pulse. The temporal evolution of photo-induced thermal strain in a material can be studied by
time resolved x-ray diffraction (TXRD) technique1,2. TXRD is a pump probe technique in which
the sample is first excited by the ultra-short laser pulse, then the generated strain in the sample is
probed by ultra-short x-ray pulse (by recording the x-ray diffraction pattern). The temporal
evolution of strain is then studied by changing the delay between pump and probe pulses. In this
study, the ultra-short x-ray source (Cu Kα) was generated by the kHz Ti:sapphire (800 nm) laser
produced Cu plasma. The x-ray photon flux was ~ 2.5x109 photons/sr./s at a laser intensity of ~
3.3x1016 W/cm2. The sample was pumped by fundamental and SH laser pulse at a fluence of ~ 6.5
mJ/cm2.
We report a comparison of thermal strain evolution in Ge (111) sample (band gap 0.66
eV) induced by fundamental (1.5 eV) and SH (3 eV) pump beams. The maximum observed strains
with fundamental and SH pump were ~ 6.210-4 and ~ 2.910-3 occurring at ~ 50 ps and ~ 15 ps
probe delay respectively. The difference in the maximum strains and their timings is due to the
lower absorption depth of SH pump pulse. The lower absorption depth results in laser energy
deposition in less number of lattice planes initially and hence these planes experience larger strain.
The strain propagation in the sample was studied upto ~ 2 ns probe delay. At this time, the residual
strains for fundamental and SH pump were ~ 310-4 and ~ 510-4 respectively which will reduce
further with delay.
REFERENCES 1. R. Rathore, H. Singhal, and J. A. Chakera J. Appl. Phys. 2019, 105706, 126.
2. A. Rousse, C. Rischel, and J.-C. Gauthier, Rev. Mod. Phys. 2001, 17, 73.
72
Ultrafast Magnetization Dynamics in Ferromagnetic Nanodot Arrays Connected by
Nanochannels
Sourav Sahoo a, Surya Narayan Panda a, Saswati Barman b, Anjan Barman a,*, a Department of Condensed Matter Physics and Material Sciences, S. N. Bose National
Centre for Basic Sciences, Block JD, Sector III, Salt lake, Kolkata 700 106, India b Institute of Engineering and Management, Kolkata 700091, India
*Corresponding author: abarman@bose.res.in
Magnonic crystals (MCs) are periodically patterned magnetic media, the magnetic
counterparts of the photonic and phononic crystals, where spin waves act as information
carrier. Two-dimensional (2D) artificially patterned nanodot arrays have long been
interesting systems due to their interesting spin configuration, magnetization reversal
properties, spin dynamics as well as their potential applications in high density magnetic
storage, memory, logic, transistor and communication devices. Several studies have
reported the magnetization dynamics in 2D arrays of magnetostatically coupled nanodot
arrays1.
Here, we investigate the spin-wave (SW) dynamics of 2D array of square Ni80Fe20
nanodots joined by rectangular nanochannels (NCs) of the same material which directly
couple the dots via exchange interaction. The Ni80Fe20 nanodot arrays of thickness 20 nm
are fabricated by using the combination of e-beam lithography, e-beam evaporation and
ion milling on Si (100) substrate. The size (s) of the square nanodot varies as 865(S1), 660
(S2) and 465 (S3) nm and the connector length (l) as 330, 210 and 105 nm, respectively,
while the width (w) of the connector is kept fixed around 260 nm. Custom build time-
resolved magneto optical Kerr effect (TRMOKE) microscope2 is exploited to probe the
precessional dynamics. The damped nonuniform oscillation consists of multiple-frequency
modes which shows high stability with bias magnetic field. Corresponding fast Fourier
transform (FFT) spectra show the presence of seven, five and three distinct SW modes for
the array S1, S2 and S3 respectively. The SW mode numbers decrease with the decrease in
dot size and the NC length. This is probably due to the modification of magnetostatic field
distribution around the edges of NCs and dots. Further, the spatial power profile of the SW
modes reveals that the presence of edge, extended, quantized and mixed quantized mode
in these systems. All the SW modes are coupled between the dots via the vertical NC
(VNC), perpendicular to applied magnetic field (H) except the highest frequency mode,
which shows a mixed behavior and the power of the mode is mainly concentrated inside
the horizontal NC (HNC), parallel to H. Inside the HNC, the highest frequency mode shows
uniform nature. This behavior is prominent for S1. Further, using numerical simulations
we show a modulation of higher frequency modes due to exchange coupling between the
dots by varying the length of the NC. The observed modulation of SW dynamics opens the
possibility of development of rich class of magnonic devices by controlling the propagation
of spin wave.
REFERENCES 1. B. Rana, D. Kumar, S. Barman, S. Pal, Y. Fukuma, Y. Otani and A. Barman, ACS
Nano, 2011, 9559, 5.
2. A. Barman, and J. Sinha, 2018, Spin Dynamics and Damping in Ferromagnetic Thin
Films and Nanostructures, (Springer Publishing AG, Switzerland).
73
CuFeS2 Quantum Dots based broadband (visible to MIR) photodetector for
detecting radiation from ultrafast sources
Nihit Saigal, Anumol Sugathan, Guru Pratheep Rajasekar and Anshu Pandey
Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore-560012
We report the characterization of a p-n junction photodetector based on a heterostructure
comprised of heavily doped n-type Silicon and p-type CuFeS2 quantum dots films. We
measure the photoresponse of the device using femtosecond visible and near infrared
(NIR) light obtained by feeding the fundamental output of a 100 femtosecond laser into
an optical parametric amplifier. The device is shown to have a very broadband
photoresponse, extending from visible (500nm) to near infrared (2200nm) wavelengths.
The device shows fast time response (~35µs) in NIR. It shows a non-linear dependence
of the photocurrent on the pulsed excitation power in the NIR region. This behavior has
been understood by invoking the mechanism of defect filling due to photogenerated
charge carriers. We further characterize the mid infrared (MIR) response of the device
using radiation from a source heated to 200-300 oC. The device response at MIR
wavelengths is slower and is understood to be bolometric in nature.
74
Ultrafast Spin-Wave Dynamics in Ferromagnetic Diamond Antidot Lattice
Koustuv Dutta, Anulekha De, Arundhati Adhikari and Anjan Barman*
Department of Condensed Matter Physics and Material Sciences, S N Bose National Centre for Basic
Sciences, Block-JD, Sector-III, Salt Lake, Kolkata-700106, India. *Email address: abarman@bose.res.in
Over last few decades, both fundamental and application-oriented research have
gained immense interest in studying the ultrafast spin dynamics of magnetic nanostructures
to meet with the ever-increasing demand in the information storage, memory and
processing industry. Manipulation of spin in one-, two- or three-dimensional peridically
patterned nanostructures (magnonic crystals) have great application potential in the on-
chip data processing and communication devices. In a typical two-dimensional antidot
lattice (ADL), a distinct class of Magnonic Crystals, nanohole arrays are arranged in a
particular lattice symmetry giving rise to a specific type of configurational anisotropy and
it can significantly modulate the spin-wave propagation and localization in that system1.
Here, we present an all-optical femtosecond time-resolved study of two-dimensional
diamond shaped Ni80Fe20 (permalloy) antidot lattice arranged in square and hexagonal
lattice symmetry (Fig. 1(a)). A custom-built Time-resolved Magneto-Optical Kerr Effect
(TRMOKE) microscope2 set-up based on two-colour colinear pump-probe geometry has
been employed for the present study. The samples have been fabricated using the e-beam
lithography followed by e-beam evaporation process. Experimental studies unfold a rich
variation of spin-wave dynamics with the change of the strength and orientation of the
applied bias magnetic field. The configurational anisotropy of hexagonal lattice displays a
complex pattern due to superposition of anisotropic contribution on behalf of nanohole
shape and lattice symmetry which significantly differs from the four-fold anisotropy of the
square lattice (Fig. 1(b)-(c)). These experimental observations are reproduced by
micromagnetic simulation. The calculated spin-wave mode profiles and internal field
distributions underpins the observed anisotropic behaviour of spin waves in such
structures.
We acknowledge financial support from S. N. Bose National Centre for Basic
Sciences (grant no.: SNB/AB/18-19/211). KD and AD acknowledge DST-INSPIRE
scheme while AA acknowledges SNBNCBS for respective research fellowships. REFERENCES:
1. R. Mandal et al., ACS Nano 2012, 6, 3397.
2. A. Barman et al., Nano Lett. 2006, 6, 2939.
Fig. 1. a) Scanning electron micrograph of the sample. Bias-field angle dependence of spin-wave frequency for d) square lattice and e) hexagonal lattice.
a)
H
x
y
ϕ
0 45 90 135 180
6
8
10
12
M1
M2
M3
M4
M5
Fre
qu
en
cy (
GH
z)
Bias Field Angle (degree)
b)
0 45 90 135 1806
8
10
12
M1
M2
M3
M4
M5
Fre
qu
en
cy (
GH
z)
Bias Field Angle (degree)
c)
75
Understanding Optical Behaviour of InP Based Core Alloy Shell QDs through
Ultrafast dynamics and Single Particle Spectroscopy
Chayan Kumar Dea, Prasun K. Mandal*a,b aDepartment of Chemical Sciences, bCentre for Advanced Functional Materials, Indian Institute of Science
Education and Research (IISER) Kolkata, Mohanpur, West Bengal, 741246, India.
E-mail: ckd12ip019@iiserkol.ac.in, prasunchem@iiserkol.ac.in*
InP based core alloy shell (CAS) QDs with high photoluminescence quantum yield
(PLQY~65%) have been synthesized using ‘one pot hot injection’ method. These newly
developed CAS QDs possess a compositionally smoothened and softened interface which
provides enhanced confinement for the photogenerated charge-carriers, excellent
photochemical stability and lesser number of trap state at core shell interface.1 It has been
observed that smoothing out the confinement potential can decrease the Auger
recombination rate by more than three orders of magnitude in comparison to an abrupt
confinement potential boundary.2 As a result blinking of QDs which is mainly originate
from non-radiative Auger recombination has been found to be suppressed in CAS QDs
than CS QDs.2,3
Spectral (steady state optical behaviour (PLQY)) and temporal (excited-state decay
dynamics) optical behaviour of different colour emitting InP based CAS QDs could be
successfully correlated at the ensemble level. The role of each time component of
multiexponential decay could be understood reasonably well.1 Rate of charge carrier
detrapping/ rate of charge carrier trapping (a single particle property) has been correlated
with PLQY (an ensemble property) for differently emitting CAS QDs. Suppression of
blinking has been achieved with small sized InP based QDs in reduced air atomphere which
is very rare for InP based QDs.3 Moreover, it has been shown that for InP based CAS QD
and core/shell (CS) QD with similar ensemble properties like similar emission maxima
(555 nm), similar PLQY (~ 65%), and similar PL lifetime, CAS QD is optically far superior
to CS QD at the single particle level.
Excitation wavelength dependent PLQY of InP based CAS QDs, which is an
apparent violation of Vavilov rule has been investigated in detail using femtosecond
ultrafast pump-probe dynamics at ensemble level for different excitation wavelengths.
Lower normalized transient population (ΔA/A) and slower exciton (predominantly
electron) relaxation at lower wavelength excitation indicates that hot exciton trapping is
more prominent at lower wavelength excitation. From excitation wavelength dependent
single particle blinking measurement it has been observed that trapping gets suppressed
and detrapping gets enhanced with increasing excitation wavelength. Similar observation
has been noted for CdSe based QDs.4 All these observations are in line with the
enhancement of the PLQY with increasing excitation wavelength.
REFERENCES
1. C. K. De, T. Routh, D. Roy, S. Mandal, P. K. Mandal, J. Phys. Chem. C, 2018, 122, 964-973.
2. Y.S. Park, W. K. Bae, T. Baker, J. Lim, V. I. Klimov, Nano Lett. 2015, 15, 7319-28.
3. C. K. De, D. Roy, S. Mandal, P. K. Mandal, J. Phys. Chem. Lett, 2019, 10, 4030-4038.
4. D. Roy, A. Das, C. K. De, S. Mandal, P. R. Bangal, P. K. Mandal, J. Phys. Chem. C 2019, 123, 6922-
6933.
76
Ultrafast Response of Nanoplatelets Around its Particle Plasmon Resonance: Effect of Size
Distribution
Asha Singh,1, a) Salahuddin Khan1 and J. Jayabalan1,2
1Nano Science Laboratory, Materials Science Section, Raja Ramanna Centre for Advanced Technology,
Indore, India-452013. 2Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai, India - 400085.
a)Corresponding author: asha@rrcat.gov.in
The optical response of metal nanostructures plays a key role in deciding the operation of plasmonic devices.
For operating at different wavelengths it is essential to tune the localized surface plasmon resonance (LSPR)
and this can be done by controlling the aspect ratio of the nanoparticles [1]. LSPR of small silver nanospheres
is less sensitive to its diameter distribution whereas other shapes do show stronger dependence on size
distribution since LSPR depends on aspect ratio. Fig-1 shows the extinction coefficient of colloidal solution
of silver nanoplatelets in water. The in-plane dipole peak occurs at 784 nm. The TEM images show an average
diameter and thickness of the nanoplatelets were 43 nm and 7 nm respectively. Degenerate transient
transmission measurements were carried out using ~190 fs, 82 MHz repetition laser operated in the range
760 nm to 830 nm (Fig-2). The peak intensity at all the wavelengths were kept constant (~0.5 MWmm-2).
The magnitude of transient transmission (|T/T|) at all wavelength shows an increase with the arrival of the
pump and decays subsequently with increasing delay (Fig-2) [2]. The sign of T/T was found to be negative
for wavelengths longer than LSPR. The maximum change in the |T/T| (|T/T|pk) shows a dip near to the
LSPR peak (Fig-3). Using a theoretical model and experimental results, we show that the observed variation
in the peak response is caused by the size distribution as well as the dispersion of nonlinear response of
nanoplatelets [3, 4]. This leads to a minima of |T/T|pk near the LSPR wavelength.
Fig-1: The extinction spectrum of the silver colloid. Inset shows TEM image of the sample.
Fig-2: Transient transmission through the sample at different wavelengths.
Fig-3: The dependence of peak change in transmission with pump-probe wavelength.
REFERENCES
1. Z. Starowicz, R. Wojnarowska-Nowak, P. Ozga, and E. M. Sheregii, Colloid and polymer
science, 296, 1029 (2018).
2. J. Jayabalan, Asha Singh, Rama Chari, Salahuddin Khan, Himanshu Srivastava, and S. M. Oak,
Appl. Phy. Lett., 94, 181902 (2009).
3. X. Zhang, C. Huang, M. Wang, P. Huang, X. He and Z. Wei, scientific reports., 8, 10499 (2018).
J. Jayabalan, Opt. Soc. Am. B., 28, 2448 (2011).
77
Singlet Fission within Ultrafast Time Scale and near Unity Yield in 5,12–bis
(phenylethynyl)tetracene thin film
Amitabha Nandia,b, Biswajit Mannaa, and Rajib Ghosha
anandi@barc.gov.in aRadiation and Photochemistry Division, Bhabha Atomic Research Center, Mumbai 400085, India bHomi Bhabha Nation Institute, Training School Complex, Anushakti Nagar, Mumbai, 400094, India
5,12–bis (phenylethynyl)tetracene (BPET) thinfilm, having thickness of 100 nm,
was prepared following thremal evaporation method. Steady state absorption measurement
shows ~80 nm red shift of absorption band (as compared to that of the monomer) and well
coverage of solar spectrum. Interestingly, the BPEA thinfilm observed to show three order
less emission yield as compared to its monomeric form. The time resolved emission
studyies also indicates singlet lifetime reduction from 7.3 ns to ~1 ps, as the sample changes
from monomer to thinfilm. To unravel the asoociated fast exciton deactivation mechanism,
ultrafast pump-probe experiments were carried out. As evident from the figure 1A and 1B,
immediately after photoexcitation the singlet excitons goes for prompt decay with lifetime
of 0.8 ps (the excited state absorption 670-740 nm). It causes formation of a meta stable
state which is assigned as triplet correlated pair state having excited state absorption (ESA)
in the 520-600 nm wavelength region. The triplet correlated pair state further undergoes
for some structural relaxation in the initial 10 ps time sacle. This is ensured from the
observed red shift of maximum of the associated ESA band. With further time delay, we
observe enhancement in ground state bleach (GSB) signal at 610-650 nm and a
concomitent growth of ESA band in the 580-620 nm region. This is associated with the
seperated triplet excition production with the time constant of ~18 ps. Simulteneous growth
of triplet ESA band (580-620 nm) and GSB signal (610-650 nm) is the signature of
presence of singlet fission process in the BPET thinfilm sample. The singlet fission yield
was estimated to be about 94%. The high singlet fission yield and well coverage of solar
spectrum by the thinfilm sample of this commercially available dye may appear very useful
for photovoltaic application.
-0.02
0.00
0.02
0.04
0.1 ps
0.5 ps
2 ps
5 ps
10 ps
A
bso
rpti
on
(O
D)
Wavelength (nm)
1A
500 600 700
-0.01
0.00
0.01
0.02
10 ps
20 ps
50ps
100ps
0
15
30560nm:- 2.3(-0.0145), 240(-0.0158)
0
5
10
600nm, :- 2.3(-0.0061), 19.2(0.012), 250(-0.0091)
0
2
4
6
A
bs
orp
tio
n (
OD
)
730nm, :- 0.78(-0.0067), 15(-0.00085)
0 10 20 30 40 60 120 180
-10.0
-7.5
-5.0
-2.5660nm, :- 3.5(0.0057), 17.7(-0.0068), 240(0.0076)
Time (ps)
1B
Figure 1: (1A) Transient absorption spectra recorded at different delay times for BPET
thin film after excitation with 390 nm light (1B) temporal profiles along with fitted data.
78
Cosolvents at Aqueous Interface: As Observed by “Classical” and “Heterodyne-
Detected” Vibrational Sum Frequency Generation Spectroscopy
Subhadip Roy, and Jahur A. Mondal* Radiation and Photochemistry Division, BARC, HBNI, Mumbai-400085,
Email-mondal@barc.gov.in
Aqueous interface plays critical roles in diverse fields, including atmospheric, chemical,
biology and applied aspects. Preferential adsorption of cosolvents, ions, and amphiphiles
as well as their mutual interactions create a unique environment at the interface, leading to
interface-specific chemical reactions. Advanced laser spectroscopy, such as sum frequency
generation, provided a molecular level understanding of the interaction of charged
amphiphiles and ions at the aqueous interface. However, the corresponding knowledge for
the cosolvent is limited. Here, we show that cosolvents, such as alcohol and ether, affect
the average hydrogen-bonding and preferred orientation of interfacial water negligibly but
the interface becomes increasingly dry (decreased water content) with increasing cosolvent
concentration.
We investigated the effect of small alcohols and ethers, which are used as cosolvents, at
the air-water interface using “narrowband classical” as well as “broadband heterodyne-
detected” vibrational sum frequency generation (C-VSFG and HD-VSFG) and surface
tensiometry techniques.1-3 Details of the VSFG setup will be discussed during the
presentation. The C-VSFG provides information about the packing and conformational
change of the cosolvents by measuring the high resolution |χ(2)|2 spectrum (χ(2) is the second
order electric susceptibility at the interface) of their sharp CH-stretch bands (2800-3000
cm-1), while the HD-VSFG measurements elucidate the ordering of interfacial water by
monitoring the imaginary-χ(2) signal of its broad OH stretch band (3000-3600 cm-1). Figure
1 shows the HD-VSFG results of the air-water-propanol interface (Imχ(2) spectra of other
amphiphiles and the corresponding C-VSFG (|χ(2)|2) results are not shown) for different
proportions of alcohol and water. The negative CH-stretch signal (2800-3000 cm-1; Figure
1) shows the methyl-up orientation of propanol at the air-water interface.2 With increasing
propanol concentration, the signal in the CH stretch region does not increase, but that in
the OH stretch region (3000-3600 cm-1) decreases without significant change in band
shape. At the neat air-alcohol interface, the signal in the CH stretch region is similar to that
of the diluted air-water-alcohol system; but that in the OH
stretch region is almost zero. This shows that the alcohol-OH
has negligible contribution in the measured interfacial
spectra. Accordingly, the decreased OH stretch signal (3000-
3600 cm-1) suggests reduced water content of the interface
for the alcohol-water mixture. In other words, the interface
dehydrates in presence of alcohol (or ether; results not
shown) as a cosolvent in water.
REFERENCES
1. Du, Q.; Superfine, R.; Freysz, E.; Shen, Y. R. Phys Rev. Lett. 1993,
70, 2313
2. Nihonyanagi, S.; Yamaguchi, S.; Tahara, T. J.Chem. Phys. 2009, 130, 204704
3. Ahmed, M.; Namboodiri, V.; Mathi, P.; Singh, A. K.; Mondal, Jahur. A.. J. Phys. Chem. C 2016, 120
(19), 10252-10260
Figure 1. Imspectra of the air-water-
propanol interface at different bulk
concentrations of propanol.
79
Cold Target Recoil Ion Momentum Spectroscopy: Design and Simulation
Swetapuspa Soumyashree, Rituparna Das, R.K. Kushawaha
Physical Research Laboratory, Ahmedabad, swetapuspa@prl.res.in, kushawaha@prl.res.in
For understanding the fragmentation dynamics of molecular ions induced by the
femtosecond laser (800 nm, 1 kHz, 25 fs), a novel electron-ion coincidence momentum
imaging technique “Cold Target Recoil Ion Momentum Spectrometer (COLTRIMS)”
setup is under development at PRL Ahmedabad. The ion and electron momentum imaging
technique is based on two Wiley-McLaren type spectrometers which consist of 16
extraction plates, two drift tubes and two position sensitive detectors (Figure 1). From the
measurement of the time of flight and position of impact for each charged particle, the
momentum vectors are determined.
Designing of the spectrometer and the simulation of the ion trajectories are carried out
using SIMION 8.0 package. For the energy and mass resolution of the spectrometer, a
MATLAB code was written to find the FWHM of time of flight profile of given ion. Figure
1 shows the ion trajectories of 10000 particles of energy 2eV in this spectrometer. The
electron and ion trajectories simulation, energy range and mass resolution will be
presented. This Setup will be combined with femtosecond pump-probe setup. Preliminary
calibration TOF results will be presented in this conference.
Figure 1. Ion trajectory simulation in COLTRIMS setup
REFERENCES
1. R. Dörner et al., Physics Reports 2000, 330, 95-192
W. C. Wiley and I. H. McLaren, Rev. Sci. Instrum. 1955, 26, 1150–1156
80
Study of molecular alignment using femtosecond laser pulses
Madhusudhan P, Rituparna Das, Pranav Bharadwaj, Swetapuspa Soumyashree, Pooja
Chandravanshi, and Rajesh K Kushawaha Atomic, Molecular, and Optical Physics, Physical Research Laboratory, Ahmedabad
madhusudhanp@prl.res.in
kushawaha@prl.res.in
In the process of observing and controlling molecular dynamics in gas phase,
angular momentum of molecules takes precedence1. Controlling the evolution of angular
momentum would be reflected as the control of molecular rotation. Dynamic alignment of
molecules using an ultrashort laser source would facilitate in the measurements. Alignment
of N2 and CO2 molecules using femtosecond laser (25fs, 1Khz, 10mJ) in pump-probe
scheme and Velocity Map Imaging spectrometer2 has been performed. Theoretical
analysis3 of the alignment has been performed considering various experimental
parameters4, and simulated using a program developed in-house. The results on molecular
alignment are presented in this conference.
REFERENCES
1. Richard N. Zare. Wiley-Interscience. 1988, Angular Momentum: Understanding Spatial Aspects in
Chemistry and Physics.
2. Kling, N. G., Paul, D., Gura, A., Laurent, G., De, S., Li, H., ... & Litvinyuk, I. V. Journal of
Instrumentation. (2014), 9(05), P05005.
3. Zhang, S., Lu, C., Jia, T., Wang, Z., & Sun, Z, Phys. Rev. A. 2011, 043410, 83.
4. Xioming Ren, Kansas State University. 2013, Laser-driven rotational dynamics of gas-phase
molecules: control and applications.
81
Anomalous Halogen–Halogen Interaction Assists Radial Chromophoric Assembly
Remya Ramakrishnan,†a Niyas M. A.,†a Vishnu Vijay,a Ebin Sebastian,a Mahesh
Hariharanb a School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Vithura,
Thiruvananthapuram, Kerala, India 695551
b Faculty of Chemistry, School of Chemistry, Indian Institute of Science Education and Research
Thiruvananthapuram, Vithura, Thiruvananthapuram, Kerala, India 695551, mahesh@iisertvm.ac.in † These authors contributed equally
ABSTRACT: The engineering of highly efficient supramolecular architectures that
mimic competent natural systems n a comprehensive knowledge of noncovalent
interactions. Halogen bonding is an excellent noncovalent interaction that forms
halogen−halogen (X2) as well as trihalogen interacting synthons.1 Herein, we report the
first observation of a symmetric radial assembly of 1,8-dibromonaphthalene(2,6-
diisopropylphenyl)imide (NIBr2) (R3̅c space group) composed of a stable hexabromine
interacting synthon (Br6) that further push the limits of our understanding on the nature,
role, and potential of noncovalent halogen bonding.2 Contrary to the destabilization
proposed for Type-I X2 interactions,3 Br6-synthon-possessing Type-I X2 interactions
exhibit a stabilizing nature owing to the exchange-correlation component. The radial
assembly of chromophores is further strengthened by intermolecular through-space charge
transfer interaction. The radial assembly of chromophores is additionally strengthened by
an intermolecular charge transfer interaction between the 2,6-diisopropylphenyl moiety
and naphthalimide core. Crystalline NIBr2 exhibits room temperature phosphorescence
with a lifetime of 23 μs. The femtosecond transient absorption spectra of NIBr2 in
chloroform captured the ultrafast intersystem crossing from the singlet to triplet state (kisc
= 7.33 × 1010 s−1) and nanosecond transient absorption spectra exhibited spectroscopic
signatures of the triplet state of the chromophore ( t = 3.1 μs) at 400 and 500 nm. Br6-
synthon-driven 3-fold symmetric radial assembly render a lattice structure that reminisces
the chromophoric arrangement in the light harvesting system 2 of purple bacteria.
REFERENCES
1. G. Cavallo, P. Metrangolo, R. Milani, T. Pilati, A. Priimagi, G. Resnati, G. Terraneo, Chem. Rev.
2016, 116, 2478.
2. M. A.Niyas, R. Ramakrishnan, V. Vijay, E. Sebastian, M. Hariharan, J. Am. Chem. Soc. 2019,
141, 4536−4540.
S.Tothadi, S. Joseph, G. R. Desiraju, Cryst. Growth Des. 2013, 13, 3242.
82
Excited state structural dynamics of 4-cyano-4’-hydroxystilbene: deciphering the
signatures of proton-coupled electron transfer using ultrafast Raman loss
spectroscopy
Reshma Mathew,a Surajit Kayal,b Adithya Lakshmanna Yapamanuc* a School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Vithura,
Thiruvananthapuram 695551, India b School of Chemistry, University of Nottingham, Nottingham.NG7, 2RD, UK. c Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0021, Japan.
*adithya@es.hokudai.ac.jp
The Photo-initiated proton-coupled electron transfer (PCET) process plays a crucial
role in the context of light harvesting in various biological and chemical systems.
Molecular model systems are typically employed to understand the mechanisms underlying
the functioning of complex biological systems. Some molecular dyads based on the PCET
property are particularly designed to achieve efficient sunlight-to-fuel production.1 Organic
photoacids are potential sources for such applications since they exhibit enhancement in
their acidity upon photoexcitation, facilitating the mimicking of some of the biological
processes. p-hydroxybenzylideneimidazolinone (p-HBI), an organic photoacid is a key
chromophore in green fluorescence protein which exhibits green emission due to excited
state proton transfer.2
Herein, we investigate the structural changes and dynamics of 4-cyano-4’-
hydroxystilbene (CHSB) in presence of an external base, t-butylamine (TBA) using the
techniques of ultrafast transient absorption, emission and ultrafast Raman loss
spectroscopy.3 Femtosecond fluorescence up-conversion measurements of the CHSB-TBA
adduct reveal a precursor-successor relationship between the ~420 and ~530 nm emission
bands, which implies that the adduct evolves predominantly through the electron-proton
transferred state. Further, Raman measurements show a clear distinction in the dynamics
of the C=C stretch of CHSB in presence and absence of TBA in terms of the amplitude
growth (0.45 ps vs. instantaneous) and the central frequency (1584 vs. 1523 cm-1).
REFERENCES
1. J. C. Lennox, D. A. Kurtz, T. Huang, J. L. Dempsey, ACS Energy Lett., 2017, 2, 1246-1256
2. J. Dong, K. M. Solntsev, O. Poizat, L. M. Tolbert, J. Am. Chem. Soc., 2007, 129, 10084-10085.
R. Mathew, S. Kayal, A. L.Yapamanu, Phys. Chem. Chem. Phys. 2019, DOI: 10.1039/c9cp02923k.
83
Hydrocarbon Chain-Length Dependence of Solvation Dynamics in Alcohol-based
Deep Eutectic Solvents: A 2D IR Spectroscopic Investigation
Srijan Chatterjee,a Deborin Ghosh,b Tapas Haldar,c Pranab Deb,c Sushil S. Sakpal,c
Samadhan H. Deshmukh,a Somnath M. Kashid*,c and Sayan Bagchi* d
a JRF, Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, Pune b SERB-NPDF, Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, Pune c SRF, Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, Pune
d Principal Scientist, Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory,
Pune, s.bagchi@ncl.res.in
Deep eutectic solvent (DES) has gained popularity in recent years as an
environmentally benign, inexpensive alternative to organic solvents for diverse
applications in chemistry and biology.1,2 Among them, alcohol-based DESs serve as useful
media in various applications due to their significantly low viscosity as compared to other
DESs. Despite their importance as media, little is known how their solvation dynamics
change as a function of the hydrocarbon chain-length of the alcohol constituent. In order
to obtain insights into the chain-length dependence of the solvation dynamics, we have
performed two-dimensional infrared spectroscopy on three alcohol-based DESs by
systematically varying the hydrocarbon chain-length. The results reveal that the solvent
dynamics slow down monotonically with increase in the chain-length. This increase in the
dynamic timescales also show a strong correlation with the concomitant increase in the
viscosity of DESs. In addition, we have performed MD simulations to compare with the
experimental results, thereby testing the capacity of simulations to determine the
amplitudes and timescales of the structural fluctuations on fast timescales under thermal
equilibrium conditions.
REFERENCES
1. Q. Zhang, K. De Oliveira Vigier, S. Royer, F. Jérôme, Chem. Soc. Rev. 2012, 41, 7108.
E. L. Smith, A. P. Abbott, K. S. Ryder, Chem. Rev. 2014, 114, 11060.
84
Extremely Weakly Interacting O-H in the Hydration Shell of High Charge Density
Metal Ions as Observed Raman Difference with Simultaneous Curve Fitting (RD-
SCF) Spectroscopy
Animesh Patra†, Subhadip Royǂ, Subhamoy Sahaǂ, Dipak K. Palit†, Jahur A. Mondalǂ ǂRadiation & Photochemistry Division, BARC, Homi Bhabha National Institute, Mumbai †School of Chemistry, UM-DAE Centre for Excellence in Basic Sciences, Mumbai
The mutual interaction between ion and water plays a pivotal role in living and
nonliving systems. Understanding the structure of water in the metal-ion hydration shell is
essential in elucidating their reactivity. For selective extraction of the native spectral
response of water associated to a metal ion, one needs to circumvent the response of
counterion-affected water (here anion) and bulk water (ion-unaffected water). To extract
metal ion (Mz+; z = 1, 2, 3) hydration shell spectrum, we introduced Raman difference with
simultaneous curve fitting (RD-SCF) analysis. For example, to extract the Mg2+ hydration
shell spetrum (𝑆()𝑀𝑧+ ), we used MgCl2 (0.3M) solution as sample (𝑆()𝑒𝑥𝑝
), NaCl
(0.6M) solution as reference (𝑅()𝑒𝑥𝑝
) and fitted the sample spectrum using equation (1).
Then, the metal ion-affected water spectrum, (𝑆()𝑀𝑧+ ), is obtained by equation (2),
which remove the response of bulk water and that of Cl--associated water from the sample
spectrum. It is noteworthy that the effect of Na+ cation on water is negligible hence, Na+-
affected water is similar to the bulk water.
𝑆()𝑓𝑖𝑡
= ∑ (𝑎𝑛 exp (−( − 𝑛)2/2 𝑛2
)𝑛
𝑛=1+ 𝑓𝑅()
𝑒𝑥𝑝 + 𝑎0 (1)
𝑆()𝑀𝑧+
∑ (𝑎𝑛 exp (−( − 𝑛)2/2 𝑛2
)𝑛
𝑛=1= 𝑆()
𝑒𝑥𝑝 − 𝑓𝑅()𝑒𝑥𝑝 − 𝑎0 (2)
Where, 𝑓 is the fraction of 𝑅()𝑒𝑥𝑝
carried by the 𝑆()𝑒𝑥𝑝
; 𝑎𝑛,𝑛, 𝑛 are the amplitude,
peak center and fwhm of the nth component band of the multi-component fitted curve, 𝑎0
is the constant background difference between the (𝑆()𝑒𝑥𝑝
) and 𝑅()𝑒𝑥𝑝
. The RD-SCF-
extracted Lu3+ hydration shell spectrum and bulk water is shown in Fig.1 for comparison.
The higher relative intensity of 3200 cm-1 band compared to bulk water, suggesting
increased H-bonding of water in the hydration shell. Interestingly, apart from 3200 cm-1
band, there is a distinct band in the extreme high frequency region (~3600 cm-1) of the OH
stretch, which clearly manifests the existence of extremely weakly H-bonded O-H in the
hydration shell. Based on controlled experiments, such as variation of charge density,
concentration, counterions, pH, we further propose that such weakly interacting O-H is
largely confined within the surface of the first hydration shell, where a second hydration
shell water donates H-bond to the first hydration shell
water (Scheme in Fig. 1). The oxygen atom the of first
hydration shell water donates significant amount of
charge to the high charge density metal ion, consequently
become a weak H-bond acceptor, resulting the weakly H-
bond O-H in the hydration shell. Such weakly interacting
OH is observed in the hydration shell of trivalent
lanthanides, bivalent alkaline earths and even monovalent
Li+ ions. Fig. 1. Typical Raman spectra (OH stretch) of bulk water and water
in the hydration shell of high charge density metal ion (Lu3+; blue
85
curve). The scheme illustrates the strongly and weakly H-bonded water in the hydration shell.
REFERENCES
[1]. Collins, K. D., Biophysical Journal 1997, 72 , 65.
[2]. Ahmed, M.; Namboodiri, V.; Singh, A. K.; Mondal, J. A.; Sarkar, S. K., J. Phys. Chem. B 2013, 117,
16479.
86
Attosecond (10-18 second) Charge Migration
Atanu Bhattacharya
Assistant professor, Department of Inorganic and Physical Chemistry, Indian Institute of Science,
Bangalore 560012, atanub@iisc.ac.in
Our interest in viewing chemical reactions with optical pulses at ever-increasingly
shorter time scale (microsecond to femtosecond) has given birth to the modern ultrafast
science. Flash photolysis and Femtochemistry are two representative milestones in the
history of ultrafast science.1 Having followed reactions through their transition state
ultimately in the femtosecond time domain, would a further improvement in the time
resolution of flash photolysis into the attosecond regime contribute to the molecular
chemical dynamics field with new discoveries of interest to general chemistry? The subject
of my seminar will revolve around this question while addressing meaning of attosecond
time scale, role of attosecond time scale in ionized weakly bound molecular clusters and
consequences of attosecond charge migration with the help of quantum molecular
dynamics simulation and high harmonic generation spectroscopy.2,3.
REFERENCES
1. A. Zewail, The Chemical Bond: Structure and Dynamics, Academic Press, Inc. 1992.
2. Sankhabrata Chandra and Atanu Bhattacharya, "Attochemistry of Ionized Halogen,
Chalcogen, Pnicogen, and Tetrel Non-Covalent Bonded Clusters" Journal of Physical
Chemistry A, Feature Article, 2016, 120, 10057-10071.
3. Sankhabrata Chandra, Irfana Ansari, Gopal Dixit, Franck Lepine and Atanu
Bhattacharya, "Experimental Evidence of Sensitivity of the High Harmonic Generation to
the Hydrogen Bonding" Journal of Physical Chemistry A, 2019, 123, 5144-5149.
87
Energy Transfer followed by Sequential Electron Transfer in a Supramolecular
Tetrad Composed of Phenothiazine, Zinc Porphyrin, Borondipyyromethene, and
Fullerene: Charge Stabilization in “Antenna-Reaction Center” Mimic
Kanika Jain,a Francis D’Souza,*b Raghu Chitta*a,c aDepartment of Chemistry, School of Chemical Sciences & Pharmacy, Central University of Rajasthan,
Kishangarh, Dist. Ajmer, Rajasthan-305817, India. bDepartment of Chemistry, University of North Texas, 1155 Union Circle, #305070, Denton, Texas 76203-
5017, United States cDepartment of Chemistry, National Institute of Technology Warangal, Hanamkonda, Warangal, Telangana
– 506004.
In natural photosynthesis sunlight is harvested via natural antenna complexes by
creating electronic excitations and the subsequent rapid excitation energy transfer to the
reaction center followed by multistep electron transfer reactions resulting into long lived
charge separated state.1 However, artificial photosynthesis calls for broad band capturing
of light to maximize the utilization and conversion of light energy. Generation of long-
lived charged sepd. states is also one of the important criteria in developing artificial
photosynthetic reaction centers.2
In the present work, we have utilized the antenna-reaction center and the electron
transfer-hole shift idea by designing a single model compound, (PTZ)3-ZnP-
BODIPY:C60Im, in which PTZ absorbs in the UV-visible region from 290-350 nm and acts
as an energy transfer antenna and also a hole shifting entity to ZnP, BODIPY absorbs in
the visible region from 350-520 nm and acts as the energy transfer antenna to ZnP, where
ZnP absorbs in the visible region from 400-610 nm and behaves as the electron donor when
axially ligated with C60Im as the electron acceptor. As integrating PTZ, BODIPY, and ZnP
moieties onto a single platform leads to the absorption of the wavelengths from 260-620
nm, this artificial photosynthetic model is expected to, not only exhibit antenna effect by
capturing broader spectrum of sunlight but also lead to charge separation along with charge
stabilization via hole shifting process. The outcome of these findings revealed by the
steady-state absorption, fluorescence emission studies, electrochemical, and
photochemical (from femtosecond and nanosecond transient spectroscopy) studies are
presented.
REFERENCES
1. F. D'Souza, P. M. Smith, M. E. Zandler, A. L. McCarty, M. Itou, Y. Araki, O. Ito, J. Am. Chem. Soc. 2004,
126, 7898-7907.
2. G. N. Lim, E. Maligaspe,; M. E. Zandler, F. D'Souza, Chem.: Eur. J. 2014, 20, 17089-17099.
88
Squaramide Based, “Turn-on” Schiff Base Multi-analyte Sensors for Zn2+ and Cd2+:
Influence of Acetate ion and Co-operativity
Lasitha P, a G.Naresh Patwari a a Department of Chemistry, IIT Bombay, Powai, India, naresh@chem.iitb.ac.in
Squaramide based sensors are well studied in recent past1 and these molecules are used mainly in the fields of organo-catalysis2, molecular recognition3, and self-assembly4. The 3d10 configuration makes both Zn2+ and Cd2+ ion spectroscopically silent and this chemical similarity of Zn2+ and Cd2+ ion makes the selective sensing of these metal ions difficult using a single sensor5. Due to these reasons an effective multi-analyte sensor with selective sensing ability for Zn2+ and Cd2+are still under way9. For this purpose, sensing technique based on fluorescence, especially “turn-on” fluorescence has an inherent advantage over other conventional techniques owing to its simplicity in operation, ease of handling, reliability of the data and good sensitivity6.
In this work, we have synthesized novel squaramide ligands following a Schiff base condensation reaction and studied for their sensing properties. The ligands consist of functional groups such as OH and –OCH3 were compared with ligand without any functional groups. Ligands show a feeble emission in DMSO and emission quantum yield increases an order of ten (from 0.0027 to 0.041) in the presence of zinc and cadmium producing a “turn-on” fluorescence effect. The selective emission responses for zinc and cadmium makes these ligands an efficient multi-analyte sensor. The role of anions is accounted in these studies and found that acetate ions play a major role in sensing by enhancing the complexation probability in a co-operative manner. Excited-state properties of ligand-metal complexes are characterized by TCSPC and up-conversion measurements. Better selectivity of cadmium ion was observed over zinc and the ligands also show sensing properties at 70/30, DMSO/water mixture under basic medium.
Figure 1: Proposed mechanism of complex formation (Photographs of a DMSO solution
of the ligand in presence of zinc and cadmium acetate showing different emission for
each metal)
REFERENCES
1. A. Rostami, C. J. Wei, G. Guérin and M.S. Taylor, Angew. Chem. Int. Ed., 2011, 50, 2059.
2. L. Kong, N. Li, S. Zhang, X. Chen, M. Zhao, Y. Zhang and X. Wang, Org. Biomol. Chem., 2014,
12, 8656.
3. X. Wu, N. Busschaert, N. J. Wells, Y. Jiang and P. A. Gale, J. Am. Chem. Soc., 2015, 137, 1476.
4. A. Portell, M. Font-Bardia and R. Prohen, Cryst. Growth Des., 2013, 13, 4200.
5. R. Purkait, S. Dey and C. Sinhaa, New J. Chem., 2018, 42, 16653.
6. S. J. Malthus, S. A. Cameron and S. Brooke, Inorg. Chem., 2018, 57, 2480.
89
Dynamics of Preferential Solvation of 5-Aminoquinoline in Hexane-Alcohol Solvent
Mixtures
Sharmistha Das, Anindya Datta* a Department of Chemistry, IIT Bombay, adutta@iitb.ac.in
Dynamics of formation of a polar solvation layer around a polar solvent in hexane-
alcohol mixtures has been studied, using 5-Aminoquinoline (5AQ) as a fluorescent probe,
whose dipole moment is increased significantly upon photoexcitation. Significant spectral
red shift, accompanied by severe fluorescence quenching, is observed, even in solvent
mixtures with as low as mole fraction 0.01 for alcohols. These solvatochromic shifts
deviate significantly from linear behaviour in their dependence on mole fraction, indicating
dipolar enrichment and making 5AQ a good candidate for study of dynamics of formation
of the solvation shell. Fluorescence decays are emission wavelength-dependent and exhibit
nanosecond rise times at red end of emission spectra, which indicate translational diffusion
of bulk polar molecules leading to dipolar enrichment of the solvation shell of 5AQ and
consequent preferential solvation. Electrostatic stabilization and hydrogen bonding
between dipolar excited state of 5AQ and polar alcohol molecules are major driving factors
here. Time evolution of emission spectra, from that in a predominantly hexane-like
environment to that in a predominantly alcohol-like environment, takes place in
nanosecond time scale and depends on the alcohol in the mixture. This in agreement with
calculations using an existing model.
REFERENCES
1. Singh, A. K.; Das, S.; Karmakar, A.; Kumar, A.; Datta, A. Phys. Chem. Chem. Phys. 2018, 20,22320.
2. Molotsky, T.; Huppert, D. J. Phys. Chem. A 2003, 107, 2769. 3. Lerf, C.; Suppan, P. J. Chem. Soc. Faraday Trans. 1992, 88, 963.
4. Hazra, M. K.; Bagchi, B. J. Chem. Phys. 2019, 151, 084502.
5. Królicki, R.; Jarzȩba, W.; Mostafavi, M.; Lampre, I. J. Phys. Chem. A 2002, 106, 1708.
90
Excited State Dynamics of Fluorogenic Molecules
Soumyadipta Rakshit,a Souradip Dasgupta,a Anindya Datta a* a Department of Chemistry, Indian Institute of Technology Bombay, Mumbai, Maharashtra 400076,
adutta@iitb.ac.in
Fluorogenic molecules have attracted significant attention due to their potential in
chemical sensing and organic electronics. Here, we report our work on two classes of such
fluorogenic molecules.
As a first of its kind, we report a nonionic surfactant TX-100 induced unidirectional
aggregated growth of a fluorophore, Dimethyl-2,5-bis(4-
methoxyphenylamino)terephthalate (DBMPT) to produce highly luminescent nanorods.
Pure aqueous phase white light emission with CIE coordinate (0.33, 0.36) from the
DBMPT nanorods was achieved through a unique Fröster Resonance Energy Transfer
(FRET) platform with Perylene-3,4,9,10-tetracarboxylic Acid Dianhydride with a potential
light harvesting ability. This work is in collaboration with the group of Prof. Anil Kumar.
Schiff bases constitute the second class of fluorogenic molecules of our interest.
Torsional motion coupled with rapid proton transfer have been predicted to be the major
non radiative pathways contributing to the very low lifetime as well as emission intensity
of these class of molecules. In this work we have tried to hinder the rapid Excited State
Intramolecular Proton Transfer (ESIPT) of a Schiff base by complexation with Zn+2 and
Al+3. In order to have a better understanding of intramolecular quenching interactions
between the metal centres we have meticulously prepared bi and trinuclear complexes
complexes with the same ligand and went on with their ultrafast studies. The complex
interplay of torsional motion, ESIPT alongside density of states has been evoked to
rationalize these observations though further experimental findings are still on in order to
completely quantify and understand this phenomenon.
REFERENCES
1. Khan, T.; Datta, A. J. Phys. Chem. C 2017, 121 (4), 2410.
2. K. Pal, V. Sharma and A. L. Koner, Chem. Commun. 2017, 53, , 7909.
91
Efficient Generation of Ultrahigh-Contrast High-Intensity Laser Pulses
C. Aparajit a, Kamalesh Jana a, Amit D. Lad a, Yash Ved a, G. Ravindra Kumar a
a Tata Institute of Fundamental Research, 1 Homi Bhabha Road, Mumbai 400 005, India
The last few decades have seen a rapid progress in generating laser pulses with peak
intensities exceeding 1022 W/cm2. These laser pulses are used for a variety of
applications, e.g., laser-driven electron or ion acceleration, generation of high-energy x-
rays and shock waves, and laboratory astrophysics.
Most of these applications would strongly benefit or even ultimately require laser pulses
with a well-known temporal structure and a temporal intensity contrast as high as
possible. Improvement of the temporal pulse quality could be realized after the pulse
compression, e.g., with plasma mirrors, plasma shutters or by generating the second
harmonic. Compared to plasma mirrors, or plasma shutter, generation of second-
harmonic pulses is simple to work with as it requires less optical components. The last
few decades has seen a lot of interest and progress in second-harmonic generation, but
not with femtosecond (fs) pulses of high intensities (of the order of terawatt (TW)/𝑐𝑚2)
using 800 nm fundamental pulses.
We present here experimental results of second-harmonic generation (SHG) of 150 TW,
chirped-pulse amplification (CPA) based laser system, centered at 800 nm and with a
pulse duration of about 25 fs, using a 2 mm thin, 70 mm diameter, lithium triborate
(LBO) type-I SHG-crystal. For the first time, we could achieve second-harmonic
conversion efficiencies as high as 70 percent, which is really promising and opens doors
to study high intensity laser-matter interactions with ultra-high temporal contrast laser
pulses.
REFERENCES
1. Marco Hornung et. al., Appl. Sci. 2015, 5, 1970-1979.
2. David Hillier et. al., Appl. Opt. 2013, 52, 4258-4263
3. Kurumi Mori, Yusuke Tamaki, Minoru Obara, and Katsumi Midorikawa, Journal
of Applied Physics 1998, 83, 2915
4. Ildar A. Begishev, Mikhail Kalashnikov, Vladimir Karpov, Peter Nickles, and
Horst Schonnagel, J. Opt. Soc. Am. B, Vol. 21, No. 2, 2004
5. Andrew M. Weiner, Ultrafast Optics, Wiley Publication, 2008
R. W. Boyd, Nonlinear Optics, Academic Press, San Diego, CA, 2nd edition, 2003
92
Enhanced Two-Photon Activity with Extended Molecular Conjugation
Habib Ali,a Debabrata Goswamib
a Department of Chemistry, IIT Kanpur, hali@iitk.ac.in b Faculty of Chemistry, IIT Kanpur, dgoswami@iitk.ac.in
The absorption of two photons of identical or different frequencies in order to excite
a molecule from its ground to its excited state is two-photon absorption. The measured
laser intensity through a sample during two-photon absorption process follows the relation:
I(z, 𝜆) =𝐼0(𝜆)
1+𝛽(𝜆)𝐼0(𝜆)𝑧.1 Here, I0(𝜆) is the incident Gaussian laser beam profile, z is the
propagation length in medium, β(λ) is the two-photon coefficient, which is related to the
two-photon cross-section (𝜎2) as, 𝜎2 (𝜆) = 𝛽ℎ𝑣 × 103/𝑁𝐴𝑐 and is reported in GM units
that correspond to 10-50 cm4s. We use 120fs laser pulses at 800nm with 600mW average
power from a commercial Ti:Sapphire oscillator (Mira-900F) to excite various azepine
samples dissolved in dichloromethane. The samples were made to flow through a 1 mm
closed circulating cuvette to ensure that there were no cumulative pulse-to-pulse effects.
It has been conjectured that extended molecular conjugation is more favored towards two-
photon absorption.2 In this work we specifically show that two azepine like molecules
having cis-trans conjugated structures (Fig. 1) show a drastic change in their two-photon
absorption (TPA) characteristics. Conformer (a) in Fig. 1 has more extended conjugation
as compared to conformer (b) and find a strong correlation between the TPA signal and the
molecular conjugation.
(a) (b)
Figure 1: Cis-Trans isomers of the important segments of the azepine based
moieties that show drastic difference in TPA.
REFERENCES
1. K. Makhal, P. Mathur, S. Maurya, D. Goswami, J. Appl. Phys., 2017, 121, 053103.
A. Nag, D. Goswami, J Photo. Chem. Photo. Bio. A, 2009, 206, 188.
N N
93
Femtosecond time resolved, micrometer space resolved two dimensional velocity
mapping of an ultraintense laser driven solid plasma
Kamalesh Jana a*, Amit D. Lad a, Yash M. Ved a, Alex P.L. Robinson c, John Pasley b, G.
Ravindra Kumar a
a Tata Institute of Fundamental Research Dr. Homi Bhabha Road, Colaba, Mumbai-400005; b York Plasma Institute, University of York, Heslington, York YO10 5DQ, United Kingdom; cRutherford-
Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom
When an ultraintense, femtosecond laser pulse interacts with solid matter, it
produces high temperature, near solid-density, plasma. The hot dense plasma created via
different laser absorption mechanisms evolves on an ultrafast timescale. It is very important
to know the temporal evolution of the plasma density profile during a laser-plasma
interaction for better understanding of the interaction process [1]. The dynamics of the
plasma can be influenced by different processes including shock compression, rarefactions
and instabilities which in turn depend on the parameters of the interacting laser pulse like
duration, polarization, intensity etc. In recent years, efforts have been made by us and
others to get to grips with the femtosecond evolution of these plasmas [2,3,4]. All these
efforts however lacked transverse spatial information. It is well known that the transverse
evolution of the plasma is a crucial feature in intense laser-matter interaction. We present
an advance on mapping the ultrafast variation of the transverse evolution of the plasma.
Specifically, we obtain micron scale resolved velocity maps of the plasma on femtosecond
timescales. We believe that our study opens a new vista in understanding several issues
crucial for ultrafast laser excited solid plasmas. Interpretation of the results and an
appropriate model will be presented.
REFERENCES
1. R. P. Drake, High Energy Density Physics (Springer-Verlag, Berlin, Heidelberg, 2006).
2. S. Mondal et al., Phys. Rev. Lett. 105, 105002 (2010).
3. K. Jana et al., Phys. Plasmas 25, 013102 (2018).
K. Jana et al., Appl. Phys. Lett. 114, 254103 (2019).
94
Design and Development of a new High Harmonic Generation (HHG) setup and
XUV beamline
Pranav Bhardwaj* ,Madhusudan*, Rituparna Das*, Pooja Chandravanshi*, Swetapuspa
Soumyashree* and Rajesh Kumar Kushawaha* * Atomic, Molecular, and Optical Physics Division, Physical Research Laboratory, Ahmedabad
bhardwaj@prl.res.in
kushawaha@prl.res.in
Design and development of a new High Harmonic Generation setup and XUV
beamline at PRL, Ahmedabad has been initiated for femtosecond and attosecond research.
The simulation has been performed in Zemax. Preliminary simulation and experimental
results will be presented at this conference.
The HHG setup comprises two vacuum chambers. One vacuum chamber is
dedicated to the HHG in which the Even-Lavie valve has been installed for generating a
pulsed atomic/molecular beam. PRL's femtolaser (25fs, 1Khz and 10mJ) pulses are focused
on the molecular beam. The HHG beam is passed through an XUV grating and HHG
spectrum is recorded using an Andor XUV camera. Optimization of laser power, gas and
phase matching has been performed to get intense XUV light. For XUV pump-IR probe
experiments, an XUV beamline has been proposed. The design and simulation results of
this beamline will be reported.
REFERENCES
1. Crane, J. K., Perry, M. D., Herman, S., & Falcone, R. W. High-field harmonic generation in
helium. Optics letters 1992, 17(18), 1256-1258.
2. Kelkensberg, F., Lefebvre, C., Siu, W., Ghafur, O., Nguyen-Dang, T. T., Atabek, O., ... & Remetter, T.
Molecular dissociative ionization and wave-packet dynamics studied using two-color XUV and IR pump-
probe spectroscopy. Physical review letters, 2009 103(12), 123005.
95
Towards Light Induced Carbocation Generation in a Supramolecular Cavity
Sunandita Paul,a and Jyotishman Dasguptaa a Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai
The timescale of primary structural changes associated with carbocation formation,
a two-electron removed transient carbon-centered intermediate, is of fundamental interest
to synthetic organic chemistry. In order to structurally track the formation of carbocations
and the subsequent equilibrating solvation timescale, ultrafast activation in confinement is
imperative. We tried to address this problem by choosing an all aromatic substrate,
tetrathiafulvalene(TTF) which has stable one-electron and two-electron oxidation states.1
TTF was confined inside a Pd6L4 12+ (where L= 2,4,6-tris(4-pyridyl)-1,3,5-triazine)
nanocage2 and the ground state of the molecule in confinement was characterized using
steady state optical spectroscopy. Neutral TTF molecule changes its molecular structure
from boat shape to form a planar aromatic TTF cation radical state. To stabilize and isolate
the radical cation form of TTF, neutral TTF powder was mixed with an aqueous solution
of Pd6L4 12+ nanocage at room temperature. Formation of a colored solution was
immediately observed which was characterized by steady state absorption, 1H NMR, EPR
and Raman spectroscopy. All the spectral features matched with literature reported TTF
radical cation3 thereby confirming that the compatible redox potentials of TTF and PdEn
cage led to the formation of a ground state radical cation in confinement. On exciting the
TTF radical cation by femtosecond pulsed laser the formation of cationic state was
observed at ~2ps which lived for around ~10ps. Further using time-resolved Raman
spectroscopy will help us unravel the timescale of the structural changes during TTF cation
generation.
REFERENCES
1. Nazario Martı´n Chem. Comm., 49, 7025, (2013)
2. Makoto Fujita Nature, 378 469, (1995)
3. J. B. Torrance Phy Rev.B Vol 19, 730 (1979)
96
High order harmonic generation from noble gases using annular laser beam
H. Singhala,b*, M. Kumara,b, A. Ansaria, and J. A. Chakeraa,b
a Homi Bhabha National Institute, Anushaktinagar, Mumbai, Maharashtra, 400 94 India. b Raja Ramanna Centre for Advanced Technology, Indore 452013, India Email *himanshu@rrcat.gov.in
Generation of high order harmonics of femtosecond laser pulses from their interaction with
gas cell is a well-established method to generate attosecond pulses. In this regard the
generation and optimization of high order harmonics from annular beam is highly
desirable, as the use of annular beams for high order harmonic generation (HHG) provides
an easy way to separate the high order harmonic radiation from the fundamental beam
without the use of any material filter. High order harmonic generation and optimization
from annular beams is not well studied, only a few reports exists in this field1,2 which
studied the HHG from annular beams in thin gas sheets1 or gas jets2. Here we report the
comparative study of HHG from the interaction of annular and Gaussian laser beams with
gas cells filled with Ar, Ne and He gases.
High order harmonics of a Ti:sapphire laser operating at 800 nm central wavelength, 1 kHz
repetition rate, 6.5 mJ energy and 45 fs pulse duration was generated by its interaction with
various gases filled in gas cell. The laser was focussed using a 750 mm focal length plano-
convex lens. Generated harmonics are then focussed using a grazing incidence toroidal
mirror and then dispersed by a flat field grating spectrograph. These harmonic orders are
then detected by a micro channel plate detector coupled with CCD camera. High order
harmonics in the range of 15th to 51st order were detected. The laser has beam diameter of
~20 mm (1/e2 intensity), annular laser beams are generated by reflecting the laser pulse
from a mirror with a circular hole of 5 mm diameter in centre.
The intensity of high order harmonics generated from the interaction of annular laser pulse
with Ar, Ne, and He gases varies between ~ 0.5x to 5x compared to the HHG from non-
annular beams. The intensity ratio between HHG from non-annular beams and annular
beams strongly depends on the laser propagation through the gas cell.
REFERENCES 1. J. Peatross, J. L. Chaloupka, and D. D. Meyerhofer Opt. Lett. 1994, 942, 19..
R. Klas, A. Kirsche, M. Tschernajew, J. Rothhardt, and J. Limpert Opt. Express 2018, 19318, 26.
97
Femtosecond Transient Absorption Dynamics of 𝝅-Extended Thioalkyl
Substituted Tetrathiafulvalene Sensitizers on TiO2 Thin Films
Chinmoy Biswas,1 K. Krishnakanth,2 N. Duvva,3 L. Giribabu,3 S. Venugopal Rao,2 Sai
Santosh Kumar Raavi1* 1 Ultrafast Photophysics and Photonics Laboratory, Department of Physics, Indian
Institute of Technology Hyderabad, Kandi 502285, Telangana 2Advanced Centre of Research in High Energy Materials (ACRHEM), University of
Hyderabad, Hyderabad 500046, Telangana, India 3 Polymers & Functional Materials Division, CSIR-Indian Institute of Chemical Technology, Tarnaka,
Hyderabad-500007, India.
Author e-mail address: sskraavi@iith.ac.in
Abstract: The excited state and electron injection dynamics of two new
organic 𝜋-extended sensitizers have been studied using femtosecond
transient absorption spectroscopy in visible region with 400 nm excitation.
The measurements were carried out for the two dyes in predominantly
neutral form in film on glass and bound on nanocrystalline mesoporous
TiO2 thin films. This study provides evidence for formation of radical
cations in dye-sensitized TiO2 films.
Keywords: Transient absorption Spectroscopy, dye-sensitized solar cell,
ultrafast charge recombination
Introduction Dye-sensitized solar cells (DSSCs) composed of a dye adsorbed on a wide band gap
semiconductor (typically TiO2 or ZnO) absorbing in the visible spectral region, are one of
the emerging solar technologies offering low production cost, easy fabrication and low
environmental impact to conventional silicon solar cells. However, a considerable progress
toward the improvement of device efficiency and stability can still be achieved through
better understanding and optimization of the fundamental charge-transfer processes[1]. In
a working DSSC, a variety of kinetically competing charge-transfer mechanisms take
place[2]. The most fundamental process in DSSCs, after the absorption of light by the dye
molecules, is the electron injection from the dye’s excited state to the conduction band of
the semiconductor[3].
Femtosecond transient absorption (TA) is a most valuable tool to observe charge
transfer dynamics taking place in liquid as well as in solid-state DSSCs. TA measurements
allow us to identify the generation of dye cations formed after injection of electrons from
the dye’s excited state to the conduction band of the semiconductor[3]. In this paper, we
present investigation of two new thioalkyl substituted tetrathiafulvalene sensitizers, G1 and
G3 by using fs-TA spectroscopy in the visible region. The structures of the sensitizers G1
and G3, their synthetic procedures and spectroscopic characterizations are reported in
literature[4]. This study provides an insight into the dynamics of the excited state, the
electron injection, and the photoinduced radical cation generation. The studies are focused
on (a) a comparison of the photodynamics in the different environments and (b) a
comparison of the photodynamics of the two dyes in order to predict which structure seems
more suitable for solar cell applications.
98
Experimental Section
In the visible region the electronic TA setup has been described in detail in literature[5].
The 800 nm and 70 fs output pulses (FWHM) of an amplified Ti:sapphire system were split
into two parts. One part was used for white light generation, from 420 to 780 nm, after
focusing into a 3 mm thick sapphire window. The other fraction was frequency doubled to
generate 400 nm excitation beam. The fluence of the excitation beam at the sample was
approximately 0.1 mJ/cm2, and its polarization was at magic angle with respect to the
probe beam. TA measurement were performed from -2 up to 4000 ps. The solid samples
were placed in a holder, which was constantly moved randomly, on a plane perpendicular
to the excitation beam. The liquid samples were measured in a 1 mm quartz cell. The TA
spectra were corrected for the chirp of the white-light probe pulses. The exponential fitting
routine did not account for wavelength dependent IRF or dispersion. Therefore, the first
ca. 300 fs were excluded from analysis, to avoid artifacts arising from the IRF.
Results and Discussion The TA spectra of the sensitizers G1 and G3 were measured on plane glass and mesoporous
substrates upon excitation at 400 nm. The Decay Associated Spectra (DAS) obtained after
a multiexponential global analysis along with the multiexponential fit of the principle
kinetic obtained from Single Value Decomposition (SVD) in global analysis of TA data
are reported in Figure 1. DASs for dye on glass film are shown in Figure 1(a) and 1(c) for
G1 and G3 respectively. While the DASs for dye on TiO2 layers are shown in Figure 1(b)
and 1(d) for G1 and G3 respectively. Figure 1(e) and 1(g) show the bi-exponential fitting
of the principal kinetics for G1 and G3 dye on glass film respectively while Figure 1(f) and
1(h) represents the 3-exponential fitting of the principal kinetics for dye on mesoporous
TiO2 layers respectively. The parameters of the TA dynamics obtained after the global
fitting are along with the UV-VIS absorption maxima of dye on TiO2 films are summarized
in Table 1. The early TA spectra on glass and TiO2 substrate are composed of a small
negative band below 550 nm, due to the bleach of the ground state population (GSB) and
a broad positive band above 550 nm which can be ascribed to excited state absorption.
With time the ESA band decreases as well as shifts to longer wavelengths. The time
evolution of the TA spectra for dye on TiO2 film could be reproduced using the sum of a
three exponential functions with 6.616, 226, and > 1700 ps time constants for G1 and 2.26,
52.56 and > 1900 ps time constants for G3 respectively. The first two shorter components
are possible associated with the decay of unrelaxed excited states, and in a more specific
way the latter could also be associated with the decay of the cation band due to fast
99
recombination of the injected electrons with the dye cations. The longest ns components
could be associated with a slow decay of the cation band.
Table 1: Parameters of TA Dynamics for the Two Sensitizers in Different Environments
upon Excitation at 400 nm obtained after multiexponential global analysis.
Conclusions
The Photophysics and electron injection dynamics of three novel D-𝝅-A organic dye have
been examined using femtosecond transient absorption spectroscopy in visible region. The
transient absorption spectra upon excitation at 400 nm provides enough evidence for the
generation of dye radical cations. The radical cations are long lived in TiO2 because of
slow back electron transfer.
References
[1] B.E. Hardin, H.J. Snaith, M.D. McGehee, Nature photonics 6 (2012) 162.
[2] A. Listorti, B. O’Regan, J.R. Durrant, Chemistry of Materials 23 (2011) 3381.
[3] S.G. Bairu, E. Mghanga, J. Hasan, S. Kola, V.J. Rao, K. Bhanuprakash, L. Giribabu,
G.P. Wiederrecht, R. da Silva, L.G. Rego, The Journal of Physical Chemistry C 117
(2013) 4824.
[4] L. Giribabu, N. Duvva, S.P. Singh, L. Han, I.M. Bedja, R.K. Gupta, A. Islam,
Materials Chemistry Frontiers 1 (2017) 460.
[5] S. Bhattacharya, C. Biswas, S.S.K. Raavi, J. Venkata Suman Krishna, N. Vamsi
Krishna, L. Giribabu, V.R. Soma, The Journal of Physical Chemistry C 123 (2019)
11118.
Dye 𝜆𝑎𝑏𝑠 𝑚𝑎𝑥 (for dye on glass)
Dye on Glass Dye on mesoporous TiO2 layers
𝜏1 (ps) 𝜏2(ps) 𝜏1(ps) 𝜏2(ps) 𝜏3(ps)
G1 431 nm 27.59 𝑝𝑠 ±4.7 𝑝𝑠
371.9 𝑝𝑠 ± 8 𝑝𝑠
6.616 𝑝𝑠 ±0.945 𝑝𝑠
226 𝑝𝑠 ± 8 𝑝𝑠
1795 𝑝𝑠 ±3𝑝𝑠
G3 464 nm 35.34 𝑝𝑠 ±4.36 𝑝𝑠
481.8 𝑝𝑠 ± 5 𝑝𝑠
2.266 𝑝𝑠 ±0.280 𝑝𝑠
52.56 𝑝𝑠 ±5𝑝𝑠
1900𝑝𝑠 ±3𝑝𝑠
Figure 1: Left panel-Decay associated spectra obtained from multi-exponential global
analysis: (a) and (b) for G1 dye and (c) and (d) for G3 dye on plane glass substrate and
mesoporous TiO2 layers respectively. Right panel- multi-exponential fit of principle SVD
component: (e) and (f) for G1 dye and (c) and (d) for G3 dye on plane glass and mesoporous
TiO2 layers respectively.
100
Effect of charge state on the ultrafast dynamics of molecular rotor
Sukriti Santra,a,b Aruna K Mora,a Sukhendu Natha a Radiation & Photochemistry Division, Bhabha Atomic Research Center, Mumbai-400085
b Center for Excellence for Basic Sciences, Kalina campus, Mumbai
9-(2-carboxy-2-cyanovinyl)julolidine (CCVJ), a well known ultrafast molecular
rotor (UMR), is extensively used to measure the microviscosity of complex chemical and
biological samples.1,2 We have investigated the detailed excited state dynamics of CCVJ
in molecular solvents to understand its excited state torsional dynamics that is primarily
responsible for its viscosity sensing behaviour. Due to the presence of carboxylic group,
CCVJ can present either in the anionic or neutral form depending on the pH of the solution.
Our detailed studies show that the excited state dynamics of neutral CCVJ is significantly
different from the anionic form. The emission quantum yield of neutral form is
significantly lower than anion. Further the excited state lifetime is relatively shorter for
neutral CCVJ than its anion (cf. figure 1A). Detailed emission wavelength dependent
excited state dynamics have been performed for both prototropic forms of CCVJ using
femtosecond upconversion technique. From time resolved emission spectra (TRES) of
these two forms of CCVJ it is observed that the excited state torsional dynamics is
significantly faster for neutral CCVJ than its anionic counterpart. This result indicates that
neutral form of CCVJ is better molecular rotor as compared to the anionic form. Hence,
the modulation of the emission intensity due to the change in the viscosity of the medium
is relatively stronger for neutral CCVJ than anionic form. Forster-Hoffmann analysis of the
viscosity dependent excited state lifetime results in the viscosity coefficient values of 0.62
and 0.46 for neutral and anionic CCVJ, respectively (cf. figure 1B). Higher viscosity
coefficient value clearly indicates that the neutral form of CCVJ is much better viscosity
sensor than its anionic form.
Figure 1A. Fluorescence spectra of CCVJ in anionic and neutral form Inset: Fluorescence intensity decays
of CCVJ in both prototropic forms. B. Emission transients of neutral CCVJ in acetonitrile-ethylene glycol
mixtures. Inset: Forster-Hoffmann plot of CCVJ for anionic and neutral forms.
REFERENCES
1. Haidekker, M. A.; Theodorakis, E. A. Molecular Org. Biomol. Chem. 2007, 5, 1669-1678.
2. Iwaki, T.; Torigoe, C.; Noji, M.; Nakanishi, M. Biochemistry 1993, 32, 7589-7592
101
High-Harmonic generation from spin-polarised defects in solids
Mrudul M S,a Nicolas Tancogne-Dejean,b Angel Rubio,b and Gopal Dixit a a Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076 b Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761
Hamburg, Germany
Generation of high-order harmonics in gases enabled to probe the attosecond
electron dynamics in atoms and molecules with unprecedented resolution. Extending the
techniques developed originally for atomic and molecular gases to solid state materials
requires a fundamental understanding of the physics at place that has been recently only
partially addressed theoretically. Here we employ time-dependent density-functional
theory to investigate how the electron dynamics resulting in high-harmonic emission in
monolayer hexagonal boron nitride is affected by the presence of vacancies. We show how
these realistic spin-polarised defects modify the harmonic emission, and demonstrate that
important differences exist between harmonics from a pristine solid and a defected-solid.
In particular, we found that the different spin channels are affected differently because of
the presence of the spin-polarised point defect, and that localisation of the wavefunction,
the geometry of the defect and the electron-electron interaction are all important
ingredients to describe high-harmonic generation in defected-solids.
REFERENCES
1. Mrudul M S et. al, arXiv preprint, arXiv:1906.10224 (2019).
102
Probing molecular chirality via laser-induced electronic fluxes
Sucharita Giri,a ,b Alexandra Maxi Dudzinski,b,c
Jean Christophe Tremblay,b,d and Gopal Dixit a
a Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 India b Institut für Chemie und Biochemie, Freie Universität Berlin, 14195 Berlin, Germany c Institut NEEL CNRS/UGA UPR2940, 38042 Grenoble cedex 9, France d Laboratoire de Physique et Chimie Théoriques, CNRS-Université de Lorraine, 57070 Metz, France
The present work focuses on understanding the conditions required to modify
the chirality during ultrafast electronic motion by bringing enantiomers out-of-
equilibrium. Different kinds of ultrashort linearly-polarised laser pulses are used to drive
an ultrafast charge migration process by the excitation of a small number of low-lying
excited states from the ground electronic state of S- and R-epoxypropane.
Control over chiral electron dynamics is achieved by choosing the different orientations
of the linearly polarised pulse. We find that chirality breaking electric fields are only
possible in oriented molecules, and that charge migration remains chiral when the
polarisation of the field lies in the mirror plane defining the enantiomer pair, or when it is
strictly perpendicular to it. Ultimately, the presence or the absence of a mirror symmetry
for the enantiomer pair in the external field
determines the chiral properties of the charge migration process.
REFERENCES
1. S. Giri, A. M. Dudzinsky, J. C. Tremblay, and G. Dixit, arXiv preprint arXiv:1909.10740 (2019).
103
Characterizing Laguerre-Gaussian pulses using Angle-resolved Attosecond
Streaking
Irfana Neyaz Ansaria and Gopal Dixitb a Department of Physics, Indian Institute of Technology Bombay, Mumbai, India, irfana@phy.iitb.ac.in b Department of Physics, Indian Institute of Technology Bombay, Mumbai, India, gdixit@phy.iitb.ac.in
Photons can carry orbital angular momentum, along with the spin angular momentum, due
to their spatial structure. The presence of this extra angular momentum has been exploited
extensively such as for nanoparticle trapping, quantum state engineering in Bose-Einstein
condensates, and chiral recognition in molecules. Here, we have proposed a strategy to
directly characterize the orbital angular momentum of the Laguerre-Gaussian (LG) pulse.
The technique, called as attosecond streaking, involves photo-emission of an electron from
the hydrogen atom by XUV- LG pulse, which are then deflected in angular spatial
directions by circularly polarized IR pulse. We have shown that the units of orbital angular
momentum present in LG pulse is directly reflected in the angle-resolved streaking spectra.
104
The curious case of warfarin photophysics Sushil S. Sakpal,a Deborin Ghosh,b Sayan Bagchi* c
a SRF,CSIR-NCL,Pune.
b SERB-NPDF, CSIR-NCL,Pune.
c Principal Scientist, Physical and Materials chemistry division, CSIR-NCL Pune, s.bagchi@ncl.res.in
Warfarin is an important oral anticoagulant drug that explores the diversity of its
surrounding environment.Warfarin binds to a specific site of Human Serum Albumin
(HSA) and acts as a probe in the competitive binding of other drugs to the HSA.In the
earlier reports of warfarin in organic solvents and aqueous based environments, multiple
UV-visible absorption peaks were assigned to different structural conformations of
warfarin. Here, we report a systematic study of warfarin and its different derivatives using
spectroscopic measurements and quantum chemical calculations to demonstrate that the
multiple absorption peaks do not arise from different isomers. We show that coumarin
moiety of warfarin is majorly responsible for the absorption spectrum, where transition
involving higher excited states give rise to the multiple absorption peaks. As coumarin
moiety is present in a variety of drugs, our study will be helpful to understand the
interaction of warfarin and other coumarin based drugs in the different drug-receptor
complex.
105
IR-IR control of High Harmonic Generation
Ankur Mandal,a Kamal P. Singhb a Department of Physical Sciences, Indian Institute of Science Education and Research Mohali, India,
ankur@iisermohali.ac.in b Department of Physical Sciences, Indian Institute of Science Education and Research Mohali, India,
kpsingh@iisermohali.ac.in
We numerically investigate IR-IR time delayed pulse on the control of HHG. We
observe a very rich variety of structures in HHG yield with respect to harmonic order and
delay. We isolate different effects such as effect of intensity and identify trajectories of
electron corresponding to each structure and identify the effect of quantum path
interference in HHG. We observe a tilt in the near cut-off harmonics, splitting towards
lower orders. This demonstrates an all optical control of HHG. 1
REFERENCES:
1. Carsten Winterfeldt, C. Spielmann, G. Gerber, Rev. Mod. Phys. 2008, 80, 117.
106
Temporal evolution of radiative rate reveals the localization of holes in
CuInS2-based quantum dots Arpita Mukherjee, Biswajit Bhattacharyya and Anshu Pandey
Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore-560012, India
In recent years the study of ternary (I − III − VI2) chalcopyrite nanocrystals have
gained increasing attentions due to their low toxicity compared to Cd and Pb based
quantum dots. Furthermore the bulk band gap (1.5eV), size-dependent tunable emission
from visible to NIR region, long exciton-lifetime (generally in hundreds of nanoseconds)
make them promising in various applications especially in photovoltaics. In addition, these
materials possess broad photoluminescence emission spectra and there is a large stoke-shift
between the emission and absorption maxima. The aforesaid properties of these
nanocrystals suggest a strong localization of the charge carriers in intra-gap states. Here
we investigate the hole localization dynamics in CuInS2/ CdS quantum dot ensembles
using time-resolved up-conversion luminescence (UPL) and transient absorption (TA)
spectroscopy. Although the TA data suggest that the electron remains in the conduction
band, the temporal evolution of the spontaneous lifetime evaluated from UPL
measurements (from 46 ns to 294 ns) infers the collapse of the hole wave function. We
further investigate the hole localization dynamics in these QDs using a model based on
simple harmonic oscillator in configuration space. Using the model, the absorption and
emission characteristics of these systems are analyzed. We compute that the transfer rate
of hole from the valence band to the defect states (~1012 s-1). The model explains the defect-
related emission broadening and the stokes shift. We also evaluate the evolution in
emission lifetimes, which is consistent with the experimental data.
REFERENCES:
1. Arpita Mukherjee, Biswajit Bhattacharyya and Anshu Pandey, Nano Futures, 2018, 2, 045007
2. under preparation