Observation of intramolecular vibrational redistribution and vibrational cooling in S1 trans-stilbene and 2-phenylindene in solution

Picosecond resonance Raman spectra of the S1 states of trans-stilbene and its torsionally hindered analog 2-phenylindene in solution show that the vibrational cooling times in these two systems are similar. Anti-Stokes scattering from high frequency modes is observed for the first time and provides a direct observation of the IVR process. The data allow us to place a lower limit of 3–5 ps for the IVR time in trans-stilbene. These results provide significant new insight into ultrafast vibrational dynamics in solution and demonstrate the utility of time-resolved Raman spectroscopy as a probe of both intra- and inter-molecular energy transfer.