Comparative study of stimulated proton-transfer luminescence of three chromones

The contrasting behavior of three related chromones with respect to amplified spontaneous emission (ASE) and laser action as intramolecular proton-transfer laser systems at room temperature is investigated. The intramolecular proton-transfer laser is considered a chemical laser in which the excited tautomer species is produced by a chemical reaction after photon-pumping activating a four-level laser system. The three chromones studied are 2-methyl-3-hydroxychromone, 2-phenyl-3-hydroxychromone (3-hydroxyflavone), and the natural product fisetin (3,3{prime},4{prime},7-tetrahydroxyflavone), each of which exhibits good proton-transfer fluorescences in the 500-nm region, with respective quantum yields of 0.29 (MCH), 0.36 (MCH), and 0.16 (dioxane). Low-temperature spectroscopic study and picosecond transient absorption spectroscopy reveals that fluorescence quenching from molecular aggregation and transient parasitic S{sub n}{prime} {l arrow} S{sub 1}{prime} absorption of the tautomer both contribute to nonobservability of ASE and lasing action in the 2-methyl-3-hydroxychromone, in contrast to excellent ASE/lasing characteristics of the 3-hydroxyflavone and fisetin under comparable conditions.