Femtosecond dynamics of electron transfer in a neutral organic mixed-valence compound

Abstract

In this article we report a femtosecond time-resolved transient absorption study of a neutral organic mixed-valence (MV) compound with the aim to gain insight into its charge-transfer dynamics upon optical excitation. The back-electron transfer was investigated in five different solvents, toluene, dibutyl ether, methyl- tert-butyl ether (MTBE), benzonitrile and n-hexane. In the pump step, the molecule was excited at 760 nm and 850 nm into the intervalence charge-transfer band. The resulting transients can be described by two time constant. We assign one time constant to the rearrangement of solvent molecules in the charge-transfer state and the second time constant to back-electron transfer to the electronic ground state. Back-electron transfer rates range from 1.5 × 10 12 s −1 in benzonitrile through 8.3 × 10 11 s −1 in MTBE, around 1.6 × 10 11 s −1 in dibutylether and toluene and to 3.8 × 10 9 s −1 in n-hexane.