Distributed decay kinetics of charge separated state in solid film

Photoinduced electron transfer in solid films of porphyrin–fullerene dyads was studied using femtosecond pump–probe method. The relaxation of the main photo-product, intramolecular exciplex, was found to be essentially non-exponential. To analyze the decays a model accounting for a distribution of the free or reorganization energies is proposed. The model allows to fit the experimental data using three parameters: non-disturbed time constant, τ0, width of the energy distribution, ΔE, and sensitivity parameter, a = −(Δ G0 + λ0)/2λ0, where ΔG0 and λ0 are the average free and reorganization energies, respectively. The parameters were found to be τ0 = 50 ps, ΔE = 0.09 eV and a = 2 for the exciplex relaxation.