Ultrafast vibrational evolution of excited-state coumarin 153 using fs/ps CARS as a transient Raman probe

摘要

The development of techniques to study molecular vibrations with reasonable frequency resolution in the femtosecond time regime for excitedstate molecules has opened new avenues of research for the understanding ofmolecular structure following electronic excitation. Frequency resolution allowsone to observe directly the evolution of vibrational modes as a function of somerelevant time delay without the need to apply Fourier Transform techniques orto separate complicated beat patterns to determine pairs of involved modes.Here, vibrational evolution upon electronic excitation in coumarin 153 (C153)is observed using a transient Raman probe technique developed in ourlaboratory that is a variation of time-resolved coherent anti-Stokes Ramanspec troscopy (TR-CARS). The technique, named fs/ps CARS, is described indetail elsewhere 1. C153 has been extensively studied for its idealsolva tochromic properties upon excitation that allow it to be used as a probe forsolvent reorganization. However, despite the wealth of work done on thesolvation properties, only a few studies have been undertaken to understand the molecular changes of the solute molecule upon electronic excitation.