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The solvation effect component of the phenomenological model of solvent effects is applied to ET(30), the molar transition energy of the Dimroth–Reichardt betaine, in binary aqueous–organic solvents. The dependence of ET(30) on x2, the mole fraction of organic cosolvent, can be quantitatively described for all 17 systems studied. New data are given for 9 of these systems. It is found that a 1-parameter model suffices to describe the composition dependence of the highly polar cosolvents, whereas a 2-parameter model is needed to account for other cosolvents, which yield a nonhyperbolic composition dependence. The solvation parameters, which are exchange equilibrium constants, yield correlations suggesting their positive dependence on cosolvent hydrophobicity and electron-pair donor ability.
Skwierczynski et al. (Sat,) studied this question.