COMMENTS CONCERNING SOLVENT EFFECTS ON CHEMICAL PROCESSES .7. QUANTITATIVE DESCRIPTION OF THE COMPOSITION DEPENDENCE OF THE SOLVENT POLARITY MEASURE E(T)(30) IN BINARY AQUEOUS-ORGANIC SOLVENT MIXTURES

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.