AM1 STUDY OF THE ELECTRONIC-STRUCTURE OF COUMARINS

We report our calculations on a series of coumarin molecules. Using semiempirical methods with an AMI parametrization, we have calculated the ground-state, first excited triplet state, and first excited singlet state energies and dipole moments as well as their dependence on the geometries of different labile side groups. We find that for all of the coumarins there are excited triplet states in close energetic proximity to the excited singlet states, and the relative ordering of these states depends on the substituents attached to the coumarin chromophore.