Spectroscopic studies of excited-state intramolecular proton transfer in 1-(acylamino)anthraquinones
作者:Terrance P. Smith、Krzysztof A. Zaklika、Khalid Thakur、Gilbert C. Walker、Keisuke Tominaga、Paul F. Barbara
DOI:10.1021/j100178a038
日期:1991.12
The excited-state properties of 1-(acylamino)anthraquinones have been examined using a variety of physical techniques, including static fluorescence spectroscopy, and picosecond and subpicosecond time-resolved fluorescence techniques, as well as picosecond transient absorption spectroscopy. The decay of the singlet excited states is dominated by a combination of efficient internal conversion via excited-state intramolecular proton transfer (ESIPT) and rapid intersystem crossing. For strongly electron withdrawing substituents, the short singlet excited state lifetimes of ca. 100 +/- 50 ps are ascribed to efficient nonradiative processes in the ESIPT tautomer. For acetylamino and heptanoylamino derivatives in cyclohexane, the anomalously short singlet lifetimes are attributable to fast intersystem crossing and formation of the triplet excited state. Subpicosecond resolution fluorescence studies show that there is an instrument-limited rise of red (ESIPT) emission on the 100-300-fs time scale for 1-(dichloroacetylamino)anthraquinone, faster that solvent relaxation. For 1-(chloroacetylamino)anthraquinone, a slower rise in blue (normal tautomer) emission is seen. Calculations and comparisons to related systems show that the tunneling splittings, solvent reorganization energies (for moderately polar solvents), and kT at room temperature are all on the same order of magnitude, giving rise to a subtle interplay among these factors.