Spectroscopic characterization and aggregation of azine compounds in different media

Abstract

In this study, we have reported for the first time a complete experimental investigation on the compound Neutral Red and the new monobrominated derivative in different media as a function of the concentration. These compounds belong to the quinone-imine class of dyes and have good potential to be applied as photosensitizers in Photodynamic Therapy. Although the aggregation of Neutral Red has been reported by several authors, this has not been thoroughly evaluated due to spectral changes occurring depending on the solvent and concentration of dye. We investigated and compared the effects of aggregation properties in water, ethanol, water–ethanol mixtures, water-polyethylene glycol 400 (75:25 v/v) and N,N-dimethylformamide. An analysis of the changes in the absorption spectra with respect to the solvent as a function of dye concentration together with theoretical calculations confirmed the monomeric species and the formation of different types of aggregates in this class of compounds.