Time dependent solvent effects on the T-1-T-n absorption spectra of thioxanthone: a picosecond investigation

Time resolved absorption (expressed by the shift of the wavenumber of maxim um absorption nu(TT)(0) --> nu(TT)(infinity)) of a probe (thioxanthone) in its triplet state ((TX)-T-3) is investigated in different solvents, using p icosecond absorption experiments. By increasing the solvent polarity, nu(TT )(infinity) is blue shifted due to a decrease of the dipole moment upon exc itation and linearly depends on the empirical polarity parameter E-T(30). M oreover, application of the solvatochromic comparison method (SCM) (pi*, al pha, beta) shows that specific interactions are prevailing in alcohols. On the contrary, nu(TT)(0) is red shifted and correlates linearly well with th e classical function of the refractive index (n): 2(n(2) - 1)/2n(2) + 1. In hydroxylic solvents, the solvent response function C(t) is described by a monoexponential tau(TX). Comparison of tau(TX) with other values concerning either probes in the singlet state or solvent characteristic relaxation ti mes underlines the key role of the specific (TX)-T-3 solvent hydrogen bondi ng. (C) 1999 Elsevier Science S.A. All rights reserved.