Abstract
Photoisomerization of azobenzene is one of the most fundamental chemical reactions. However, its mechanism has not fully elucidated because the reaction proceeds in a very short time as short as 1 picosecond. We carried out a systematic study of ultrafast photochemical dynamics of azobenzene with S2(ππ*) photoexcitaiton using several types of femto/picosecond time-resolved spectroscopy. It was revealed that the isomerization takes place in the lowest excited singlet (S1) state even in the case of S2 excitation, which has significantly revised the isomerization mechanism believed so far.
