PM3 study of the electronic spectra of some substituted aminocoumarins

The photophysical properties of some 7-aminocoumarins have been investigated by PM3/CI method. Solvent effects have been evaluated by the continuum reaction field approach. The results show that all the molecules emit from a planar internal charge transfer (ICT) state. Radiationless decay occurs via the twisted ICT state, no evidence of a deactivation path via pyramidalization of the amino group has been found. Computed potential energy barriers for the torsional motion of the amino group are in line with the observed rate constants for nonradiative decay.