Vibrational‐Mode‐Selective Modulation of Electronic Excitation

Abstract

Vibrational‐mode‐selective modulation of electronic excitation is conducted with a synchronized femtosecond (fs) visible (vis) pulse and a picosecond (ps) infrared (IR) pulse. The mechanism of modulation of vibrational and vibronic relaxation behavior of excited state is investigated with ultrafast vis/IR, IR/IR, and vis‐IR/IR transient spectroscopy, optical gating experiments and theoretical calculations. An organic molecule, 4'‐(N,N‐dimethylamino)‐3‐methoxyflavone (DMA3MHF) is chosen as the model system. Upon 1608 cm‐1 excitation, the skeleton stretching vibration of DMA3MHF is energized, which can significantly increase the Franck‐Condon factor for electronic transition, facilitate the radiative decay and promote emission from vibrational excited states. As results, a remarkable enhancement and a slight blueshift in fluorescence are observed. The mode‐selective modulation of electronic excitation is not limited in luminescence or photophysics. It is expected to be widely applicable in tuning many photochemical processes.