Determinação das Propriedades Fotofísicas e Fotoquímicas de Corantes Fenotiazínicos em Misturas Binárias de Água/Solvente Orgânico.

Abstract

This study has evaluated the behavior of the methylene blue (MB) and its analogues dissolved in binary mixtures of water/organic solvent with respect to the effect of the concentration of dyes, substituents on dye structures and polarity of solvents. It was observed that the concentration of dye in the medium leads to an increase in the intensity of absorption. Furthermore, the increase of the concentration of dye in aqueous medium has shown the effect of aggregation of dyes. In general, the increasing solvent polarity results in a bathochromic shift of the maximum wavelength of the absorption band of the monomeric specie. On the other hand, the increasing content of demethylation of the amino groups of dyes leads to a hypsochromic shift of the wavelength of absorption of the monomeric specie in aqueous medium. The values obtained for the rotational time of the MB dye in pure solvents are in the following the order: r acetonitrile < r ethanol < r glycerol. These results are in agreement with the order of the solvent viscosity: η acetonitrile < η ethanol < η glycerol. Thus, it was observed that the increasing rotational time is clearly influenced by the viscosity parameter. Concerning to the fluorescence lifetime of the MB and 1,9-dimethyl methylene blue (DMMB) in binary mixtures of water/organic solvent, lower lifetimes were observed for mixtures containing higher water content, which can be assigned to the effect of solvent polarity.