Formation and solvation dynamics of electrons in polyols

Abstract

Using pump-probe transient absorption spectroscopy we studied the solvation dynamics of the electron in liquid polyalcohols: ethane-1,2-diol, propane-1,2-diol, propane-1,3-diol and propane-1,2,3-triol. First, transmission measurements allowed us to assess that electrons were produced via two-photon ionization of the solvent with 263 nm femtosecond laser pulses, and to determine the two-photon absorption coefficient of the polyols. Second, time-resolved absorption spectra ranging from 440 to 710 nm were measured. Our study shows that the excess electron in the diols presents an intense and wide absorption band in the visible and near-IR spectral domain at early time after photoionization. Then, for the first tens of picoseconds the electron spectrum shifts toward the blue domain and its bandwidth decreases as the red part of the initial spectrum drops rapidly while the blue part hardly evolves. Using Bayesian data analysis method, the observed picosecond solvation dynamics were reconstructed with three models: a two-step mechanism and two continuous relaxation models. Comparison between the ability of models to reproduce the experimental kinetics is in favor of a heterogeneous continuous relaxation. Recent results obtained in propane-1,2,3-triol show that the electron solvation dynamics is very fast in this solvent despite its high viscosity and highlight the role of the OH group in that process.