Real-time spectroscopy of excited states in azobenzene

Abstract The photoisomerization dynamics of 4-(dimethylamino)azobenze in solution was studied by pump–probe spectroscopy using sub-5 fs laser. Negatively- and positively-chirped pulses were used to selectively excite vibrationally coherent wave-packets in the ground and excited states, respectively. Time dependence of instantaneous frequencies of C–N and NN stretching modes was obtained by time–frequency analysis of transmittance-change traces with high-time resolution. In the excited state, clear correlation of frequency modulation at the period of about 400 fs between these two modes were observed and the dynamic mode coupling is discussed.