Spectroscopy of amplified spontaneous emission laser spikes in polyhydroxyflavones

Research spectroscopy on some polyhydroxyflavones has revealed extraordinary wavelength red-shifts for the amplified spontaneous emission (ASE) laser spikes, displaced from the corresponding proton-transfer fluorescence maxima. The shifts observed are 150 cm(-1) for 3-hydroxyflavone, 740 cm(-1) for 3,4',7-trihvdroxyflavone, and 1070 cm(-1) for 3,3',4',7-tetrahydroxyflavone in dioxane at 298 K (excited by the third harmonic of Nd:YAG laser, 15.5 mJ). The unorthodox shifts are interpreted as arising from intermolecular dipolar field perturbation effects associated with the high population of the proton-transfer tautomer lowest excited state. The zwitterion structure of the proton-transfer tautomer is treated as the origin of the extraordinarily large dipole moments, modulated by extra hydroxy group substitution. Variations of solvent dielectric constant, solute concentration, and the pumping Nd:YAG laser energy support the mechanism given for the ASE laser spike shift.