Comments concerning solvent effects on chemical processes. Part 7. Quantitative description of the composition dependence of the solvent polarity measure ET(30) in binary aqueous–organic solvent mixtures

Abstract

A recently published two-step solvational model for mathematically describing the spectral properties of the Dimroth–Reichardt betaine dye E_T in binary aqueous–organic solvent mixtures is critically examined in the light of fundamental spectroscopic principles. The published spectroscopic method is found to be inconsistent with the Beer–Lambert relationship with regard to absorption additivity in solutions containing multiple light-absorbing solvational chromophores. Two alternative data treatments are presented for describing the spectral properties of the E_T betaine dye. The first treatment is consistent with both the Khossravi–Connors–Skwierczynski two-step solvational model and fundamental spectroscopic principles. The second treatment assumes that only a single solvational chromophore is present in solution, and the observed absorption wavelength shift is described using the nearly ideal binary solvent (NIBS) model.