A study on photo-induced intramolecular electron-transfer in fullerene-benzothiadiazole-triphenylamine using time-dependent density functional theory

We employed first-principle calculations to study the photo-induced electron transfer (PIET) process of a fullerene-benzothiadiazole-triphenylamine (C60-BTD-TPA), fullerene-diphenylbenzothiadiazole-triphenylamine (C60-PBTD-TPA), and fullerene-triphenylamine (C60-TPA). The ground state geometries of C60-BTD-TPA, C60-PBTD-TPA, and C60-TPA were optimized using density functional theory (DFT). Their excited states were investigated using time-dependent HF, and time-dependent DFT (TDDFT) methods. The long-range corrected CAM-B3LYP functional was found to give the best agreements with the experimentally observed transition energies. CAM-B3LYP-based wave functions were also employed to calculate the charge transfer integrals using generalized Mulliken–Hush (GMH) approach, and the photo-induced charge separation (kCS) and charge recombination rate constants (kCR) were calculated using Marcus theory. The results showed the calculated kCS and observed kCS of C60-PBTD-TPA and C60-TPA correspond to each other, however, the both of C60-BTD-TPA differ by two orders of magnitude. For kCR of these compounds, the calculated and observed values were more contrary to each other due to improper application of Marcus electron-transfer theory.

The illuminated state of C60-BTD-TPA corresponding to the electron transition of 314 → 319 and the charge separated states of C60-BTD-TPA corresponding to the electron transition of 314 → 315.Figure optionsDownload as PowerPoint slideHighlights
► We investigated theoretically the excited states of the 60-BTD-TPA, C60-PBTD-TPA, and C60-TPA.
► We found the CAM-B3LYP functional was proper to calculate the transition energies.
► The charge transfer integrals were calculated using GMH approach.
► The calculated kCS using Marcus theory were roughly consistent with the observed values.