| The proton transfer dynamics of 3-hydroxyflavone (3-HF) and lumcihrome were investigated using picosecond time-resolved spectroscopy. The excited-state proton transfer of 3-HF exhibited a very rapid, single exponential risetime of the tautomer species in very pure hydrocarbon solvents. A slight temperature dependence was observed: a risetime less than 10 ps at room temperature increasing to ca. 40 ps at 77K.;The excited-state proton transfer of lumichrome in two different solvent systems was investigated. In varying concentrations of pyridine in p-dioxane, lumichrome exhibited two different rates of proton transfer inferred from two risetimes of the tautomer species. In both cases, a pyridinium cation transported the proton. The two rates resulted from different orientations of the pyridine in the lumichrome-pyridine, ground-state complexes.;Acetic acid in ethanol comprised the second solvent system in which the excited-state, proton-transfer of lumichrome was investigated. In this solvent system, three different rates of proton transfer were detected. Two different rates were inferred from a biexponential decay of the normal fluorescence. From a more rapid, tautomer risetime, faster than 10 ps, the remaining, third rate of proton transfer was deduced. While the acetic acid, doubly hydrogen bonded to the lumichrome, promotes the proton transfer, different acetic acid-lumichrome, ground-state complexes were responsible for the different rates of proton transfer.;The ground-state proton transfer of 3-HF was investigated using transient absorption spectroscopy. Stimulated emission pumping (SEP) was used to induce a significant, ground-state tautomer population. Two absorption profile series, without and with SEP, exhibited identical absorption bands. The rise and decay of the absorption bands mimicked the known rise and decay of the tautomer emission, and were therefore, attributed to absorption by the excited-state tautomer. The rate of the ground-state proton transfer was inferred to be less than 30 ps, the time required for the SEP process, since no different absorption profile was observed in the two different, absorption series. |
