Excite d state electric dipole moment of thiazine dyes: A compar ative stud y

A quantitative study of the sol vent effect on the photophysical properties of two cationic thiazine dyes , Methylene blue , Thionine was carefully carried out at room tem perature. T he electronic absorptio n and emis sion spectra of the dye s were rec orded in various organic solvents with differe nt polarity at room tem perature. The ground state and the excited state dipole m oments of the dyes w ere estimated from solv atochromic shifts of a bsorption an d fluoresce nce spectra. The solvent dependen t spectral shifts in absorption and fluorescen ce spectra w ere analyzed by the Kamlet-Taft parameters.