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Photoinduced Electron Transfer in a Donor-Acceptor Dyad Amy Ferreira August 14 th, 2007.

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  • Slide 1
  • Photoinduced Electron Transfer in a Donor-Acceptor Dyad Amy Ferreira August 14 th, 2007
  • Slide 2
  • Outline Introduction Background Applications Charge Transfer Quarterthiophene-Anthraquinone (T4-AQ) Spectroscopic properties Experimental results Future goals
  • Slide 3
  • Background and Applications Thiophenes Have potential in photovoltaic cells, light emitting diodes, and thin film transistors Photosynthesis Photosynthesis occurs with no back electron transfer, while it still occurs in most man-made systems. Charge transfer Charge transfer through peptide bonds Long range charge transfer
  • Slide 4
  • D A ee D +. A . Electron transfer et E D+D+ AA E DA Ground State Charge transfer (CT) state
  • Slide 5
  • E LUMO HOMO D A Photoinduced electron transfer D* Locally excited (LE) state et E LUMO HOMO D+D+ AA Charge transfer (CT) state
  • Slide 6
  • Electron transfer D A D +. A . G = G G 0 i G 0 = G 0 f G 0 i E q i f H if transition state Marcus and Sutin Biochim. Biophys. Acta 1985, 811, 265.
  • Slide 7
  • Electron transfer D A D +. A . G0G0 GG E q i f
  • Slide 8
  • Photoinduced electron transfer D A D +. A . G0G0 GG E q i f D* A h
  • Slide 9
  • Normal vs. Inverted region
  • Slide 10
  • Jablonski Diagram T4*-AQ T4-AQ CT State KfKf Absorbance K nd K et = k CS K bet = k CR E
  • Slide 11
  • Quarterthiophene-Anthraquinone ee Model Compound T4-COOH (Quarterthiophene-carboxylic acid) Test Compound T4-AQ (Quarterthiophene-Anthraquinone)
  • Slide 12
  • Quantum Yield
  • Slide 13
  • Lifetime T4-AQ T4a Scatterer T4-AQ T4a Scatterer
  • Slide 14
  • Experimental Results Solvent ( , n) Compound a (max) / nm f (max) / nm ff / nsk f c 10 9 / s -1 k nd c 10 9 / s -1 HexaneT4-COOH 392487 0.210.529 0.0410.401.5 (2.0, 1.38)T4-AQ3914700.260.527 0.0140.501.4 TetrachloromethaneT4-COOH 401500 0.17 0.631 0.0530.271.3 (2.2, 1.46)T4-AQ3944960.180.596 0.0150.311.4 TolueneT4-COOH3945060.180.522 0.0360.351.6 (2.4, 1.50)T4-AQ4025010.110.785 0.0160.141.1 ChloroformT4-COOH 4045050.120.474 0.0230.261.9 (4.8, 1.45)T4-AQ394510 EthylacetateT4-COOH 4005000.170.504 0.0370.331.7 (6.0, 1.37)T4-AQ391496 TetrahydrofuranT4-COOH4065010.180.5581 0.0430.321.5 (7.5, 1.41)T4-AQ384494 DichloromethaneT4-COOH3955130.140.540 0.0410.261.6 (9.1, 1.44)T4-AQ400493 AcetoneT4-COOH3874990.140.581 0.0010.241.5 (22, 1.36)T4-AQ400496 AcetonitrileT4-COOH3864980.0560.631 0.0530.0891.5 (38, 1.34)T4-AQ400494
  • Slide 15
  • T4-COOH in Toluene T4-AQ in Toluene Femtosecond Flash Photolysis Absorbance
  • Slide 16
  • T4-COOH in Acetonitrile T4-AQ in Acetonitrile
  • Slide 17
  • Femtosecond Flash Photolysis Lifetime T4-AQ in Acetonitrile T4-COOH in Toluene T4-AQ in Toluene
  • Slide 18
  • Experimental Results Solvent out / eV G et (0) / eV G bet (0) /eV Hexane0.06144291.24599 4.04599 Tetrachlromethane0.0441769 1.00292 3.80292 Toluene0.0540527 0.854122 3.654122 Chloroform0.526537 0.187432 2.612568 Ethylacetate0.710502 0.398511 2.401489 Tetrahydrofurane0.724188 0.564164 2.235836 Dichloromethane0.717626 0.678385 2.121615 Acetone0.961557 0.996453 1.803547 Acetonitrile1.03181 1.09567 1.70433 FC: Frank Condon factor : Reorganization energy W: Coulombic factor G (0) : Driving force G s : Electrode potential correction = E 00 : 0-0 electron transition = CS (ps) k CS (x 10 11 s -1 ) CR (ps) k CR (x 10 11 s -1 ) Toluene Chloroform4.72.1730.14 Dichloromethane1.28.3150.67 Acetonitrile0.7141.37.7
  • Slide 19
  • Experimental Results
  • Slide 20
  • Conclusions Solvent Polarity Charge transfer properties have a strong dependence on the polarity of the solvent Charge Recombination Although the driving forces were large, the rates of charge recombination were 2-20 times slower than that of photoinduced charge separation Inverted Marcus Region The decrease in the electron-transfer rate constants with the increase in the driving forces for the three solvents suggests that the charge recombination processes occur in the inverted Marcus regions for the particular media
  • Slide 21
  • Future goals Long range charge transfer In proteins, efficient charge transfer cannot occur over 1.5nm, but we aim to prepare a system that mediates charge transfer over several nanometers Currently we are preparing the redox species to affix to the sides of non-native -L-amino acids that will mediate 3 types of charge transfer: Tunneling, electron hopping, hole hopping
  • Slide 22
  • Acknowledgements Wei Xia Valentine Vullev Duoduo Bao Jiandi Wan Radiation Lab at Notre Dame Chak Him Chow Vullevs lab group
  • Slide 23
  • Normal vs. Inverted region G0G0 G > 0 E q i f
  • Slide 24
  • G0G0 G = 0 E q i f Normal vs. Inverted region
  • Slide 25
  • G0G0 G > 0 E q i f Normal vs. Inverted region
  • Slide 26
  • Fluorometer Scheme Scheme: an example of a spectrofluorometer for lifetime and fluorescence measurements Arc Lamp Excitation Monochromator Sample Curvet Emission Monochromator Diode Laser
  • Slide 27
  • Flash Photolysis To PC Optical Delay Rail Frequency Doubler Ocean Optics S2000 CCD Detector Sample Cell Filter Wheel Chopper CLARK -MXR CPA-2010 775 nm, 1 kHz 1 mJ/pulse (7fs -1.6 ns) Probe Pump Ultrafast Systems
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