Second excited singlet state (S2) fluorescence quantum yields and lifetimes of six aromatic thiones have been measured in solution at room temperature. Intramolecular S2 S, internal conversion dominates S2 decay in inert perfluoroalkane solvents, but intermolecular photochemical and photophysical processes dominate in more strongly interacting solvents. Stern-Volmer quenching is observed when perfluoroalkane solutions of 2,2,3,3-tetramethylindanthione, a model thione, are spiked with addends at concentrations up to ca. 0.3 M. Measurements of the rate constants for the bimolecular quenching of S2 fluorescence by 26 different addends reveal that the thione S2 state is highly reactive and that the initial intermolecular interaction path divides into physical and chemical branches, the branching ratio being a function of the nature of the quencher.
A vibrational analysis for the excitation and fluorescence spectra of the S1–S0 transition in jet-cooled indole and N-deuterated indole is presented. This analysis yields the frequencies for eight low-lying S1 vibrational modes of both isotopic species. Single vibronic level fluorescence spectra also enable us to refine many of the S0 vibrational frequencies. Quantum interference effects in the energy-resolved fluorescence decays for one vibrational level of S1 indole are observed as a result of picosecond laser excitation. Through analysis of the fluorescence spectra and the modulated fluorescence decays, the coupling responsible for the quantum beats was found to result from a zero-order in-plane mode coupled to a level which is described by several zero-order out-of-plane modes. The effect of the deuterium substitution on the quantum beats is also investigated.
The excited state dynamics of 3-methylindole are investigated with the goal of further characterizing the nonadiabatic interaction giving rise to ' La-%, mixing in its excited singlet state. Both the bare molecule and its clusters with polar species display evidence of coupling between these two close-lying states. By using a series of successively more polar ligands, it is shown that the strength of the interaction between the ' Lb and 'La states can be "tuned", permitting the observation of progressive changes in excited state behavior. This enables us to relate the present results to previous studies conducted in this and a number of other laboratories. While each of these has concentrated on the measurement of a particular excited state phenomenon as a signature of 'La state coupling, the results presented here are used to show how they can be successfully integrated into a more general picture of 'La-lLb state coupling in indoles.
The time-resolved fluorescence of the lone tryptophanyl residue of ribonuclease T1 was investigated by using a mode-locked, frequency-doubled picosecond dye laser. The fluorescence decay could be characterized by a single exponential function with a lifetime of 3.9 ns. The fluorescence was readily quenched by uncharged solutes but was unaffected by iodide ion. These observations are interpreted in terms of the electrostatic properties of the amino acid residues at the active site of the protein, which would appear to restrict the access of solute species to the tryptophanyl residue. The temperature dependence of the fluorescence lifetime and anisotropy decay time could be rationalized in terms of a model which postulates a significant ordering of the solvent layer immediately surrounding the surface of the protein.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.