This article primarily reviews recent work on ultrafast experiments on excited state intramolecular electron and proton transfer, with an emphasis on experiments on chemical systems that have been analyzed theoretically. In particular, those systems that have been quantitatively characterized by static spectroscopy, which provides detailed information about the reaction potential energy surface and about other parameters that are necessary to make a direct comparison to theoretical predictions, are described.
The excited-state properties of 1-(acy1amino)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 f 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. transfer in plyatomic systems.
The rates of self-exchange for several systems of the class MCp2X+/Cp2, where M is Ru or Os and X is Cl, Br, or I, have been measured by the NMR line-broadening method. For each metal, the rates increase along the halogen series as given above and are more rapid for = Ru than for the osmium analogues. In consideration of these data, the possibility is raised that these 2e self-exchange reactions and those of other metal ions take place by le steps.
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