UNRAVELING THE SOLVATOCHROMISM OF A TRIARYLMETHANE DYE BY RESONANCE RAMAN SPECTROSCOPY

The effect of the solvent on the electronic properties of the triarylmethane dye rosolic acid (RA) is investigated by means of UV-VIS and resonance Raman (RR) spectroscopies. The comparison of the solvatochromic behavior of both neutral and dianionic species of RA in acetonitrile, dimethylsulfoxide, and methanol illustrates the effect of polarity and hydrogen bonding on their electronic transitions. The resonance Raman analysis revealed two distinct chromophores in both neutral and dianionic species: i) one located at the central carbon atom, acting as an electron acceptor, and ii) the other involving the π-system of the donor groups. The observed resonance Raman excitation profiles are solvent dependent and could be interpreted as the effect of the solvent on the planarity of the aromatic rings in relation to the central carbon atom. In the case of neutral RA species, having C2 symmetry, specific hydrogen bonding interactions are responsible for inducing a symmetry increase. The opposite effect was observed for the dianionic species [RA]2-, having D3 propeller symmetry, where the interactions with the solvent induces a lowering of the symmetry.