Effect of Excitation Pulse Carrier Frequency on Ultrafast Photoinduced Charge Transfer Kinetics: Effect of Intramolecular High Frequency Vibrational Mode Excitation

Abstract

Influence of excitation pulse carrier frequency on photoinduced ultrafast intramolecular charge transfer kinetics is investigated in the framework of a multichannel stochastic point transition model involving an excited state formation. It is supposed that an intramolecular high frequency vibrational mode being active at the excitation stage also accepts the energy at the stage of photoinduced charge transfer. A strong dependence of the photoinduced charge transfer rate constant on excitation pulse carrier frequency is uncovered. Since this dependence is associated with charge separation from different excited states of an intramolecular high frequency vibrational mode, it is named the vibrational spectral effect. The simulations show that the effect may be both positive (the photoinduced charge transfer rate constant increases with increasing the excitation pulse carrier frequency) and negative (opposite trend). In the area of low exergonicity of the photoinduced charge transfer, the effect is mostly positive, while in the field of strong exergonicity, it is mostly negative. The amplitude of the vibrational spectral effect predicted by the model is rather large and can be observed in experiments even if the vibrational relaxation/redistribution time constant is as short as 100 fs.