Solvent and pressure dependence of the absorption and fluorescence spectra of anthronitrile

Abstract

Solvent and pressure dependences of the absorption (430–300 nm) and fluorescence spectra of anthronitrile are reported and compared with earlier studies of anthracene. The origins of the solvent dependences are analyzed in terms of dielectric theories developed by McRae and by Baur and Nicol. Satisfactory fits of the experimental data are obtained, which suggest that the dipole moment of the 1 La excited singlet state of anthronitrile is 2.5±1.0 times as large as the dipole moment of the ground state. Two absorption bands at 27.4±103 and 28.8× 10 3 cm −1 (in hexane solutions) are assigned as the 1 Lb transition, and the solvent dependences of these bands are interpreted as suggesting that the dipole moment of the molecule is not changed by this transition. Although pressure dependences of the spectra of polymethylmethacrylate and polyacrylonitrile solutions of anthronitrile can be qualitatively interpreted in terms of the solvent dependences, quantitative discrepancies between the anthronitrile and anthracene results indicate that solvent shift theories based upon the dielectric continuum approximation are inadequate to explain the pressure dependences quantitatively.