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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)³
ε = 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 C60
1.01
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 C60
1.01
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
