Study of the intramolecular charge-transfer (ICT) process in 4-dimethylamino-4′- nitrostilbene by picosecond time-resolved CARS

The intramolecular charge‐transfer (ICT) process of 4‐dimethylamino‐4′‐nitrostilbene (DNS) in solution was studied by pump–probe and transient CARS experiments with a 1 ps time resolution. Whereas pump–probe experiments give good evidence for the formation of an ICT state in polar solvents, CARS experiments support structural changes associated with the ICT process. In acetonitrile, a 37 cm−1 downshift of the NO2 stretching mode can be explained by a structural change located on the acceptor NO2 group and assigned to conformational relaxation of the ICT state. In toluene, such behavior is not observed correlated with the absence of ICT state stabilization in non‐polar solvents. Copyright © 2000 John Wiley & Sons, Ltd.