Picosecond Spectroscopy Studies of the Intersystem Crossing of Aromatic Carbonyl and Nitro Compounds in Solution

The build-up time constants of Tn←T1 transition bands were measured with 4-hydroxybenzophenone, Michler’s ketone, 2-nitrofluorene, 1-nitropyrene, and 9-nitroanthracene in solution with the aid of picosecond spectroscopy. All the compounds exhibit fast build-up of the Tn←T1 absorption with the time constants smaller than 100 ps. The picosecond kinetics of these nonfluorescent compounds are interpreted in terms of the electronic structures of initial and final states relevant to radiationless transitions.