Photophysical and Photochemical Properties of 2,3-Dihydro-4(l H)- quinolinones. Part II. Rates and Mechanism of Primary Processes

Abstract Fluorescence quantum yields, singlet lifetimes and triplet yields for 2-methyl-2,3-dihydro-4(1 H)-quinolinone and N -m ethyl-2,3-dihydro-4(1 H)-quinolinone were determined as a function of temperature. In non-polar solvents, an efficient non-radiative process identified as an indirect singlet →triplet transition occurring through S 2 (n,π*) was found to depopulate the lowest S 1 (π,π*) state. In polar solvents, direct singlet → triplet intersystem crossing appears to dominate. Photochemical dehydrogenation produced the corresponding 4(1 H)-quinolinone with a yield of few times 10 -2 . This was shown to be the only traceable reaction route.