Time resolved fluorescence of N,N-dimethylaminobenzonitrile in glycerol triacetate: experimental results and model interpretation

Solvatochromic dynamics and internal charge transfer kinetics of dimethylaminobenzonitrile (DMABN) dissolved in glycerol triacetate (GTA) have been investigated by means of time resolved fluorescence spectroscopy. After pulse excitation in correspondence of the high-frequency absorption, several dynamical features of the typical dual fluorescence spectra observed for DMABN in polar solvents are revealed. A precursor-successor behaviour for the observed decay of the low-frequency band is measured. These features are rationalized, at a semi-quantitative level, in terms of a stochastic model in which coupling of the fluorescent probe with the polar environment is explicitly taken in account. Ingredients of the model are the potential energy surface for the probe internal coordinates, and hydrodynamic and dielectric properties of the solvent. The comparison of simulations and experimental observations is satisfactory, and further support is given to the interpretation of the internal charge transfer dynamics in DMABN, and homologues, as a reversible interconversion process with low intrinsic energy barrier and strong coupling to the solvent environment.