Photoinduced Charge Transfer Processes of Zinc Porphyrin Derivatives for Dye-sensitized Solar Cells

We studied the excitation energies of zinc porphyrin(ZnP) and zinc porphyrin analogues(ZnP-R) with long-range corrected(LC) density functional theory. We compared three recent LC functionals, wB97XD, CAM-B3LYP, LC-wPBE and functionals B3LYP with the experiments. It was found that the low energy excitation is well predicted for ZnP with the LC-wPBE functional based on 6-31G(d) basis set. Excited-state geometry optimizations for all the compounds were carried out. It was shown that upon the photo-excitation nearly 1 e transferred to the acceptor unitdodecafluorosubphthalocyanine, SubPc(F)₁₂] and a highly polarized state formed in compound 5. But after the relaxation of the first excited state, the electron on the acceptor went back to the ZnP a little and then shifted from ZnP to the donor segmentbis(4-hexylphenyl)amino] partially. The computed excited-state radiative lifetime(τ) for compound 5 is 943 μs, which shows a reasonable agreement with the experimental observation. According to the long-lived exciton in strong push-pull compound 5, we proposed that electron injection to semiconductor might occur after vibrational relaxation of excited state.