Population dynamics of vibrational modes in stilbene-3 upon photoexcitation to the first excited state

The vibrational energy redistribution due to the geometrical rearrangement induced by photoexcitation of stilbene-3 into the S1 state is monitored selectively with respect to the different forms of nuclear motion in this polyatomic system. The femtosecond time-resolved, pump-CARS scheme is employed to trace the population flow between vibrational modes associated with this structural rearrangement. The decay of the signal at 1189-1333 cm−1 is attributed to vibrational cooling with population flowing out of these modes, whereas the rise observed at 1600 cm−1 is attributed to reorganization of the respective bonds due to the transition from the S0 to the S1 state geometry.