SYMMETRY-BREAKING SOLVENT EFFECTS ON THE ELECTRONIC-STRUCTURE AND SPECTRA OF A SERIES OF TRIPHENYLMETHANE DYES

Solvent effects on the electronic structure of a series of para-substituted triphenylmethane dyes have been investigated using polarized Raman scattering and fluorescence spectroscopy, with interpretation aided by the results of intermediate neglect of differential overlap (INDO) molecular orbital calculations. While the evidence points to D3 symmetry for the triphenylmethane cation in solution, resonance Raman and fluorescence data indicate that the symmetry of the substituted dyes is lowered by an interaction with the solvent. Semiempirical molecular orbital calculations support the idea that interaction of a charge or dipole with one of the amino groups could be responsible for breaking the symmetry of the crystal violet and parafuchsin ion, thus lifting the degeneracy of the excited electronic state which gives rise to absorption of visible light. The splitting of the excited electronic state shows up in the polarization dependence of both the resonance Raman spectra and the fluorescence emission. INDO calculations as well as fluorescence measurements argue against the existence of two ground-state conformations, such as a symmetric and an unsymmetric propeller form, as has been previously suggested.