TRIPLET-STATE POTENTIALS IN THE COMPETITIVE EXCITATION MECHANISMS OF INTRAMOLECULAR PROTON-TRANSFER

A phenomenological analysis is given of the three cases of lowest triplet state potentials relative to ground singlet and lowest excited singlet state potentials in the presence of intramolecular proton transfer. In each case, singular excitation phenomena are observed respectively: enhanced normal tautomer molecule phosphorescence (T-1 --> S-0), dual phosphorescence, and unique proton-transfer (PT) tautomer phosphorescence (T-1' --> S-0'). The application of these model cases to proton-transfer examples involving radiation-detector scintillators, biomolecule fluorescence probes, and four-level lasers is discussed. The development of the potential curve interaction models permits the optimization of the desirable large wavelength shift and maximization of quantum yield of the PT fluorescence. The competition of normal tautomer and PT tautomer phosphorescences with the PT fluorescence is discussed as a limiting factor.