The solvent-dependent isomerization dynamics of 4-(dimethylamino) azobenzene (DMAAB) studied by subpicosecond pump-probe spectroscopy

The photoisomerization dynamics of 4-(dimethylamino)azobenzene (DMAAB) are studied using subpicosecond pump-probe spectroscopy. Following photoexcitat ion at 400 nm, resonant with the lowest-lying pi-pi* transition, excited-st ate internal conversion occurs with a time-constant of similar to 0.8 ps in acetone and ethanol, and similar to 1.4 ps in fluorotrichloromethane. Inte rnal conversion is followed by ground-state vibrational relaxation on the s imilar to 10 ps timescale. It is proposed that the solvent dependence of th e excited-state decay reflects the solvent-polarity dependence of the excit ed-to-ground-state energy gap. The results presented here, in combination w ith earlier work, suggest that rapid isomerization following photoexcitatio n into the lowest-energy electronic state is a general feature of azobenzen e photochemistry. (C) 1999 Elsevier Science B.V. AU rights reserved.