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Photoinduced Electron Transfer in Porphyrin-Fullerene Dyads : Computational Study Morteza M.Waskasi April 2015
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  • Photoinduced Electron Transfer in Porphyrin-Fullerene Dyads : Computational Study

    Morteza M.WaskasiApril 2015

  • Outline

    Porphyrin-Fullerene Dyad

    Aim of research –challenge in Porphyrin-Fullerene Dyad

    The energy level of charge separated state as function of polarity of

    solvents.

    Marcus approach to calculate the ET rate

    Charge recombination Rate in 2-MeTHF and PhCN and comparison

    with experimental results

    Summary and future work.

    2

  • Porphyrin-Fullerene Dyad

    Porphyrin

    Similar to natural chlorophyllide chromophores.

    Extensive conjugated 𝞹-system. Favourable oxidation potential.

    Large extinction coefficients in visible region.

    Fullerene

    Good combination with porphyrins as a strong electron acceptor.Remarkable electron acceptors due to their large symmetrical shape and delocalized 𝞹 -system.Fullerenes are light absorber in the visible region.

    Small reorganization energy.

    3H. Imahori, K. Hagiwara .Journal of the American Chemical Society 118, 11771–11782 (1996).

  • Challenges in ET in Porphyrin-Fullerene Dyad

    Charge recombination is in inverted regime

    Charge separation is in the normal regime

    Create long-lived charge separated state

    Retarding charge recombination

    4

    Charge recombination and charge separation occur in inverted or normal regime ?

    BELIEVED

    AIM Prove or disprove

  • Methods

    5

    Gaussian 09:Optimization Charge Internal reorganization energy

    Qchem:Optimization of Charge Separated StateCharge Calculation at Separated StateElectronic Coupling

    SolvMol: Solvent reorganization EnergySolvent Free EnergyCorrection to the experimental free energy

    D.Matyushov, Chemical Physics , 324, 172-194(2006).

  • Donor and Acceptor

    6

  • The ET rate constant calculation: Semiclassical Marcus equation

    ∆𝙶 =∆𝙶 𝘨𝘢𝘴+ ∆𝙶 𝘴

    ∆𝙶 𝘨𝘢𝘴~1.01 eV

    7

    V~0.0002 eV

    λ~0.56 eV

    A. Nitzan, Chemical Dynamics in Condensed Phases (Oxford University Press, 2006) p. 744.

  • Kodis, G.; Liddell, P. A.; Moore, A. L.; Moore, T. A.; Gust, D. J. Phys. Org. Chem., 2004, 17, 724-734.

    Ph C60

    Ph C60

    Ph C60

    1.01

    0.78

    0.78

    0. 34

    0.26

    hν0.14

    0.56

    0.56

    1.39

    1.53

    -∆G λ

    Energy Level diagram in gas and polar solvents

    1.91 eV

    0

    ∆G

    Gas

    THF

    MTHF

    PhCN

    DMF8

  • The ET rate constant calculation: Marcus equation

    λᵥ~0.146 eV

    R.C

    Ener

    gy

    9P.Barbara, T.Meyer, M. Ratner. J. Phys. Chem. 100, 13148-13168(1996)

  • Solvent Reorganization and Free Energy in MTHF

    μ= 1.38 Dα= 10 (Å)³ε = 7.6

    10

  • Energy Gap in MTHF

    11

  • Driving Force and Reorganization Energy

    -∆G

    λ

    12

  • Recombination Rate in 2-MeTHF

    Inverted regime

    Normal regime

    Inverted regime

    Normal regime

    -∆G

    Bent

    Coplanar

    Experimental result by Gerdenis Kodis ,EFRC. 13

    Energy Gap=0

    Energy Gap=0

  • Kodis, G.; Liddell, P. A.; Moore, A. L.; Moore, T. A.; Gust, D. J. Phys. Org. Chem., 2004, 17, 724-734.

    P C60

    P C60

    P C601.01

    1.58

    0. 34

    hν0.14

    ----

    1.39

    -∆G λ

    CS and CR in PhCN solvent: Inverted or Normal regime?

    1.91 eV

    0

    ∆G

    Gas

    Exp

    PhCN

    14

  • P C60

    P C60

    P C601.01

    1.58

    0. 34

    CS and CR in PhCN solvent: Inverted or Normal regime?

    1.91 eV

    0

    ∆G

    Gas

    Exp

    Emp

    15

    P C60

    P C60

    P C60

    P C60

    ∆Gcs

    ∆Gg

  • Summary

    Temperature dependence of charge recombination rate.

    Same trend of K ET for both experimental and computational

    approaches.

    Solvent reorganization energy increase and driving force decrease by

    increasing polarity of the solvents.

    The lifetime of charge separated states vary as a function of polarity of

    solvents and temperature.

    Solvent reorganization energy and driving force rush in opposite way

    by increasing T in 2-MeTHF.

    Good agreement between calculated and the experimental rate is

    found for P-C60 in 2-MeTHF solvent. 17

    Inverted regime

    Normal regime

  • Future work

    Finding other conformers of porphyrin-fullerene Dyad.

    Investigation of charge separation rate vs. temperature.

    Make a model for forward and back ET for porphyrin fullerene

    dyad and then extend it for other artificial reaction centers to

    predict the electron transfer rate as function of temperature and

    polarity of solvent.

    T. Karilainen, O. Cramariuc , J of Computational Chemistry 36, 612–621 (2015) 18


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