Solvent and Solvent Density Effects on the Spectral Shifts and the Bandwidths of the Absorption and the Resonance Raman Spectra of Phenol Blue

Abstract

We have measured the absorption and the resonance Raman spectra of a solvatochromic dye, phenol blue, in liquid and supercritical solvents. We have found anomalous solvent dependence of the absorption bandwidth in liquid solvents: the width has apparently no correlation with the absorption peak shift. On the other hand, we have found good linear correlation between the absorption peak shift and the peak position of the resonance Raman bands (the CN and the CO stretching modes). The relative intensities of the Raman bands and the bandwidth of the CN stretching mode also show correlation with the absorption peak shift. Incorporating these Raman data, the anomalous bandwidth of the absorption spectrum is explained by the change of the intramolecular vibrational contribution to the absorption bandwidth due to the electronic structure change by the solvent, which cancels the change of the solvent contribution. We have estimated the solvent reorganization energy assuming linear dependence of the intramolecular...