Effects of solvent on the electronic absorption and fluorescence spectra of quinazolines,and determination of their ground and excited singlet-state dipole moments

The electronic absorption, and fluorescence excitation and emission spectra of 11 quinazolines have been measured at room temperature (298 K) in several solvents of different polarities (cyclohexane, dioxane, ethylether, chloroform, ethylacetate, 1-butanol, 2-propanol, ethanol, methanol, acetonitrile, dimethylformamide and dimethyl sulfoxide). The effects of the solvent upon the spectral properties are discussed. Experimental ground-state dipole moments were measured for quinazolines and were used in combination with the spectral results to evaluate their first excited singlet-state dipole moments by means of the solvatochromic shift method. The theoretical ground and excited singlet-state dipole moments for selected quinazolines were calculated as a vector sum of the π-component (obtained by the PPP method) and the σ-component (obtained from σ-bond moments). A reasonable agreement was observed between the experimental and the theoretical values. Excited singlet-state dipole moments are higher than the ground-state values for most quinazolines.