title: Thermohalochromism of phenolate dyes conjugated with nitro-substituted aryl groups.
abstract: The cationic halochromism and thermohalochromism of four phenolate dyes conjugated with aryl moieties substituted with one or two nitro groups were investigated in the presence of organic (tetra-n-butylammonium bromide and benzyltriethylammonium chloride) and inorganic (sodium perchlorate) salts, in hydrogen-bond donating (water, 1-propanol, 1-butanol and 2-propanol) and hydrogen-bond accepting (acetonitrile and dimethylsulfoxide) solvents. Although a positive halochromic response was observed in water for tetraalkylammonium salts, their thermohalochromic behavior was negligible. A negative halochromic behavior was observed for the dyes in all solvents, when the added cation was Na+. Plots of Δλmaxvs. c (Na+) allowed the apparent association constants for the solvated phenolate-cation pair to be estimated. In most cases, a positive thermohalochromism was observed in the range of 25-50°C, exceptions being the more sterically hindered phenolate dyes in the less polar solvents 2-propanol and acetonitrile. The observed variations were rationalized by invoking the effect of temperature on the phenolate-cation, phenolate-solvent and cation-solvent interactions.
authors: Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile.
authors: Laura
authors: L
authors: Hermosilla
authors: Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile. Electronic address: marcos.caroli@usach.cl.
authors: Marcos Caroli
authors: MC
authors: Rezende
authors: Departamento de Química, Universidade Federal de Santa Catarina, Florianópolis, SC, Brazil.
authors: Vanderlei Gageiro
authors: VG
authors: Machado
authors: Departamento de Química, Universidade Federal de Santa Catarina, Florianópolis, SC, Brazil.
authors: Rafaela I
authors: RI
authors: Stock
keywords: Cationic halochromism; Conjugated polynitroaryl phenolate dyes; Thermohalochromism