Photo‐physical Properties of N‐methyl‐3,4‐fulleropyrrolidine and Its Derivatives: A DFT and TD‐DFT Investigation

A series of N-methyl-3,4-fulleropyrrolidine (NMFP) derivatives were designed by selecting different π-conjugated linkers and electron-donating groups as D-π-A and D-A systems. The optimised structures and photo-physical properties of NMFP and its derivatives have been determined using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods with the B3LYP functional and the 6-31G basis set. According to the computation analysis, both the π-conjugated linkers and the electron-donating groups can influence the electronic and photo-physical properties of the NMFP derivatives. Our calculated results demonstrated that the electron-donating groups, with significant electron-donating ability, had the tendency to increase the highest occupied molecular orbital (HOMO) energy. The π-conjugated linkers with lower resonance energy decreased the lowest occupied molecular orbital (LUMO) energy and caused a significant decrease in the energy gap (Eg) between the EHOMO and ELUMO. A Natural Bond Orbital (NBO) analysis examines the effect of the electron-donating group, π conjugated linker, and electron-withdrawing group for these NMFP derivatives. For the NMFP derivatives, a projected density of state (PDOS) analysis demonstrated that the electron density of HOMO and LUMO are concentrated on the electron-donating group and the π-conjugated linker, respectively. A TD-DFT/B3LYP calculation was performed to calculate the electronic absorption spectra of these NMFP derivatives. Both the electron-donating group and the π-conjugated linker contribute to the major absorption peaks, which are assigned as HOMO to LUMO transitions and are red-shifted relative to those of non-substituted NMFP.