Vibrational coherence in ultrafast electron transfer reaction observed by broadband transient absorption spectroscopy

Photoinduced electron transfer (ET) is one of the most important processes in light energy conversion systems. Marcus theory is one of the most famous frameworks on ET reaction in condensed phase. In this theory, reorganization of surrounding media is regarded as a main reaction coordinate. However, ultrafast ET beyond Marcus' framework has been reported in various systems. To elucidate the role of molecular vibration in ultrafast ET, we have investigated the ET dynamics between a naphthacene dye and aniline derivatives by means of broadband transient absorption spectroscopy. Coherent wavepacket motions of naphthacene dye with frequencies of 300-1600 cm^-1 were observed in time domain. The vibrational coherence of 310 cm^-1 mode was reduced with increasing electron transfer rate, suggesting this vibration is coupled to electron transfer reaction.