SOLVENT EFFECTS ON THE ELECTRONIC ABSORPTION AND FLUORESCENCE EMISSION-SPECTRA OF MEROCYANINE-540 - A BIOLOGICAL PROBE

The electronic absorption and fluorescence spectra of merocyanine 540 (MC-540) were determined at 298 K in several solvents of different pol arity (dioxane, toluene, triethylamine, diethyl ether, chloroform, met hyl acetate, pyridine, acetone, ethanol, methanol, nitromethane, aceto nitrile, and dimethyl sulfoxide). For the first time, the ground-state dipole moment of MC-540 was measured in dioxane-dimethylformamide (15 : 1, v/v) at 298 K. Solvent effects were evaluated using the solvatoc hromic shift method (Bakhshiev and Kawski-Chamma-Viallet correlations) . The spectral blue shifts observed with increasing solvent polarity i ndicate a slightly lower value of the dipole moment in the first excit ed singlet state as compared with the ground-state dipole moment. The application of the Kamlet-Abboud-Taft polarity parameters to the elect ronic spectral data of MC-540 is discussed.