Fluorescence spectra of trans- and cis-azobenzene – emission from the Franck–Condon state

The photodynamics of the two isomers of azobenzene in DMSO after nπ* excitation are monitored via transient absorption and steady state emission spectroscopy. The excited state decay of the cis-form is close to single-exponential with a time constant of 0.1 ps. The trans-isomer decays in a biphasic fashion with characteristic times of 0.34 and 3.0 ps. This biphasic behaviour has no impact on its fluorescence intensity. It is concluded that the fluorescence probes the dynamics in the vicinity of the Franck–Condon region.