The cleavage process of an immosulfonate was studied through time resolved laser spectroscopy. The SO-S, and SO-T, transitions were located on the oxime moiety. Under excitation, the cleavage process occured through a singlet mechanism. Under sensitized excitation, an efficient cleavage of the N-O bond occured in the triplet state of the iminosulfonate. The photoreactivity of this compound was compared to that of parent photobase generators (the O-acyloximes) based on the same oxime chromophore.