Picosecond time-dependent Stokes shift studies of fluoroprobe in liquid solution

Abstract

We report on a picosecond spectroscopic study of the dynamical Stokes shift of fluoroprobe in the lowest excited state in the solvents diethylether and ethylacetate. Time-resolved emission spectra with a time-resolution of approximately 10 ps are presented. The spectra reflect dynamical Stokes shifts of a few thousand wave numbers within 10-100 ps after the pulsed laser excitation. The time-dependent shifts are representative of the solvation dynamics of fluoroprobe in diethylether and ethylacetate.

Subpicosecond studies of the solvation dynamics of fluoroprobe in liquid solution

“…Remark that the total Stokes shift in the steady state emission of fluoroprobe dissolved in diethyl ether is about 5100 cm-~ which seems significantly different from the estimated shift of 7000-8000 cm-I in Ref. 18. However, it should be recalled that the latter numbers refers to the low temperature (T~ 160 K) results, whereas the shifts reported here are the room temperature results.…”

“…The solvation times for the fluoroprobe/ethylacetate and the fluoroprobe/diethylether solutions are shorter than those obtained previously for the same systems at lower temperatures [18]. More specifically, in diethylether r s = 1.6 ps at room temperature (this work), while at temperatures ranging from 162 to 201 K, r s decreases from 27 to 10 ps [18]. Thus the shorter time scale measurements are consistent with our previous results which showed that r~ decreases as the temperature increases.…”

“…The absorption spectrum of fluoroprobe in solution does not change as a function of the solvent used [19]. On the other hand, the emission spectra display solvatochromism characteristic of Lippert-Mataga behavior, i.e., the frequency of the emission band maximum, urea X, varies linearly with the dielectric based solvent polarity parameter Af [ 18,19]. The emission spectra of Frequency (103 cm -1) charge transfer state character of the fluorescent excited state.…”

“…Time-resolved fluorescence measurements were carried out using either the femtosecond upconversion spectrometer, detailed below, with a response function of about 300 fs (FWHM) or a time-correlated single-photon counting (SPC) setup [18], with a response function of approximately 20 ps (FWHM). The use of both setups allows us to cover a time span from hundreds of femtoseconds up to nanoseconds.…”

“…[18] and references therein). For the solvents of relevance to this work, only for ethylacetate and diethylether the r D values have been published.…”