RESONANCE RAMAN-STUDY OF SOLVENT EFFECTS ON A SERIES OF TRIARYLMETHANE DYES

Resonance Raman spectroscopy was used to address questions concerning the influence of the solvent on the structure and aggregation state of a series of triarylmethane dyes. These molecules are of interest owin g to the dramatic solvent effects exhibited in their optical absorptio n spectra, which have recently been interpreted in terms of intermolec ular interactions which perturb the D3 symmetry of the cationic dyes. Raman spectra of parafuchsin, malachite green, crystal violet and ethy l violet were compared in various solvents, in order to explore change s in the vibrational modes brought about by aggregation (in water), io n-pair formation (in non-polar solvents) and ion-dipole interactions ( in polar solution). In triply amino-substituted dyes, the data point t o the possibility that a resonance structure exists having a positive charge on one of the three nitrogens. It is discussed how the resultin g reduction in the expected D3 symmetry of the cation affects the reso nance Raman spectrum.