Tracking photoinduced bond formation dynamics by femtosecond time-resolved impulsive stimulated Raman spectroscopy

Realtime observation of nuclear rearrangements during chemical reactions is one of the ultimate goals in chemical science today. In particular, elucidation of the atomic choreography that dictates the efficient and directional chemical reactions of functional complex molecular systems is highly desired. Yet, such attempts have been largely hampered by a technical difficulty to track structural changes of condensed-phase polyatomic molecules on the time scale of nuclear motion, i.e., femto-to-picosecond time scale. In order to achieve this goal, we developed a highly sensitive time-resolved 'time-domain' Raman technique, called time-resolved impulsive stimulated Raman spectroscopy (TR-ISRS), which allows us to track structural changes of the photoreaction intermediates with femtosecond temporal resolution. With TR-ISRS, we successfully visualized key, ultrafast structural dynamics in various condensed-phase complex molecular systems. Here, we overview the basic principle and experimental aspect of TR-ISRS and present direct observation of the ultrafast bond formation dynamics in the metal complex assembly. (author)