Halochromism and solvatochromism of a π* probe in binary solvent mixtures

Abstract

Dipolarity polarizability values, π*, of 17 binary solvent mixtures of variable composition have been measured with the recently introduced probe 1. The values obtained are in good agreement with reported parameters derived previously for a few solvent mixtures, employing 4-nitroaniline and N,N-diethylnitroaniline as probes. Preferential solvation of dye 1 by the more polar component was observed for most binary mixtures. Exceptions to this behaviour were some alcoholic solvent mixtures, where 1 was preferentially solvated by the less polar alcohol. This departure from the generally observed trend was ascribed to the hydrophobic character of the bisthienyl dye. The halochromic behaviour of 1 in organic salt solutions was also investigated and rationalized in terms of dye–salt association.