Intersystem crossing and internal conversion from the lowest excited singlet state of diazanaphthalenes

Triplet quantum yields of five diazanaphthalenes in room temperature solution have been determined. These values indicate that, except in the case of quinoxaline, internal conversion competes as a nonradiative decay mechanism for the excited singlet state. Rates of intersystem crossing and internal conversion in these molecules are determined. Solvent effects on the phthalazine triplet quantum yield are interpreted in terms of perturbations on the states involved.