A QUANTITATIVE STUDY OF THE EFFECT OF SOLVENT ON THE ELECTRONIC ABSORPTION AND FLUORESCENCE-SPECTRA OF SUBSTITUTED PHENOTHIAZINES - EVALUATION OF THEIR GROUND AND EXCITED SINGLET-STATE DIPOLE-MOMENTS

Electronic absorption and fluorescence excitation and emission spectra of five phenothiazines (phenothiazine, promethazine, thionine, methyl ene blue and Azure A) were determined at room temperature (293 K) in s everal solvents of various polarities (cyclohexane, dioxane, ethyl eth er, chloroform, ethyl acetate, 1-butanol, 2-propanol, ethanol, methano l, acetonitrile, dimethylformamide and dimethyl sulfoxide). The effect of the solvents upon the spectral characteristics was studied. In com bination with the ground state dipole moments of these phenothiazines, the spectral data were used to evaluate their first excited singlet-s tate dipole moments by means of the solvatochromic shift method (Bakhs hiev's and Kawski-Chamma-Viallet correlations). The theoretical ground and excited singlet-state dipole moments for phenothiazines were calc ulated as a vector sum of the pi component (obtained by the Pariser-Pa rr-Pople method) and the sigma component (obtained from sigma-bond mom ents). A reasonable agreement was found with the experimental values. For most phenothiazines under study, excited singlet-state dipole mome nts were found to be significantly higher than their ground-state coun terparts. The application of the Kamlet-Abboud-Taft solvatochromic par ameters to the solvent effect on spectral properties of phenothiazines is discussed.