Subnanosecondhyphen;timehyphen;resolved emission spectroscopy of 1hyphen;methylindole and 2,3hyphen;dimethylindole innhyphen;butanol

摘要

Subnanosecondhyphen;timehyphen;resolved fluorescence spectra of 1hyphen;methylindole and 2,3hyphen;dimethylindole innhyphen;butanol were recorded at temperatures of 118ndash;293 K in order to elucidate the unusually large Stokes shift of indoles in polar solvents. Above 200 K the presence of an isoemissive point in the emission spectra indicates interconversion between a partially relaxed excited state (Bast; state) and a completely relaxed one (Rast; state). TheBast;rarr;Rast; process is characterized by a rate parameter identical with the inverse of the longest longitudinal dielectric relaxation time of the solvent and thus due to the collective reaction of butanol tetramers far removed from the solute. Analysis of the time evolution of the spectral shift below 200 K, reveals that theBast; emission spectrum undergoes a Bakhshievhyphen;type continuous red shift characterized by a relaxation time which compares well with the Debye relaxation time of the second dielectric dispersion region and may therefore be attributed to the rotation of a butanol monomer close to the solute molecule. As concerns the nature of the emitting states, neither the1Lbndash;1Lalevel inversion interpretation nor the1La/CT (1Lastate with increased chargendash;transfer character) interpretation is wholly consistent with the results of this investigation.