title: 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.
abstract: 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. Dyes 3a-c were used as probes to investigate binary solvent mixtures, and the synergistic behavior observed was attributed to solvent-solvent and solute-solvent interactions. A very unusual UV-vis spectroscopic behavior occurred with dye 3d, which has in its molecular structure two nitro substituents as acceptor groups and two phenyl groups on the phenolate moiety. In alcohol/water mixtures, the E(T)(3d) values increase from pure alcohol (methanol, ethanol, and propan-2-ol) until the addition of up to 80-96% water. Subsequently, the addition of a small amount of water causes a very sharp reduction in the E(T)(3d) value (for methanol, this corresponds to a bathochromic shift from 543 to 732 nm). This represents the first example of a solvatochromic switch triggered by a subtle change in the polarity of the medium, the color of the solutions being easily reversed by adding small amounts of the required cosolvent.
authors.affiliation: Departamento de Química, Universidade Federal de Santa Catarina, UFSC, CP 476, Florianópolis, Santa Catarina 88040-900, Brazil.
authors.forename: Leandro G
authors.initials: LG
authors.lastname: Nandi
authors.forename: Felipe
authors.initials: F
authors.lastname: Facin
authors.forename: Vanderléia G
authors.initials: VG
authors.lastname: Marini
authors.forename: Lizandra M
authors.initials: LM
authors.lastname: Zimmermann
authors.forename: Luciano A
authors.initials: LA
authors.lastname: Giusti
authors.forename: Robson
authors.initials: R
authors.lastname: da Silva
authors.forename: Giovanni F
authors.initials: GF
authors.lastname: Caramori
authors.forename: Vanderlei G
authors.initials: VG
authors.lastname: Machado