Nitro-substituted 4-[(phenylmethylene)imino]phenolates: solvatochromism and their use as solvatochromic switches and as probes for the investigation of preferential solvation in solvent mixtures.

Four 4-[[(4-nitrophenyl)methylene]imino]phenols (2a-d) were synthesized. After deprotonation in solution, they formed the solvatochromic phenolates 3a-d, which revealed a reversal in solvatochromism. Their UV-vis spectroscopic behavior was explained on the basis of the interaction of the dyes with the medium through combined effects, such as nonspecific solute-solvent interactions and hydrogen bonding between the solvents and the nitro and phenolate groups.