As the wavepacket moves away from the Franck-Condon region, both the SE and ESA signals exhibit significant quenching owing to the two main reasons. First, TDMs become smaller, which is a manifestation of the significance of the non-Condon effects in azobenzene . Second, IC depopulates the the excited state. After 170 fs, the S 1 population becomes small and both the SE and ESA signals tend to vanish (see Fig. ).