Vibrational‐Mode‐Selective Modulation of Electronic Excitation

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 change the shape of the absorption, 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. Mode‐selective control of molecular luminescence is achieved by Synchronous femtosecond/picosecond pulses. Typically, by energizing the skeleton vibration of excited DMA3MHF, one can significantly promotes the radiation transition process, leading to the significant enhancement of molecular fluorescence. This experiment illustrates a new approach to modulate the relaxation behavior of excited molecules and control a series of photophysical/chemical process.