Anionic merocyanine dyes based on thiazol-2-hydrazides: reverse solvatochromism, preferential solvation and multiparametric approaches to spectral shifts.

Anionic merocyanine colored dyes based on (4-nitro/cyanophenyl)-substituted thiazol-2-hydrazides (THAs), which are donor-π-acceptor type push-pull molecular systems and characterized with a strong intramolecular charge transfer (ICT) in the ground state, have been examined as reverse solvatochromic systems. THAs are shown to exhibit both positive and negative solvatochromism with a reversal of the latter occurring for solvents of E(30) value of ca. 45.