Molecular interaction of organic dyes in bulk and confined media

Molecular interactions of five thiazine dyes with increasing alkyl substitution have been studied in aqueous and microemulsion media at 303 K within a concentration range of (1.35–7.00) × 10−4 M. The dimerization constant (Kd) values for the five dyes are ranged between 1.761 and 6.258 × 103 l mol−1 in bulk water media, where as in microemulsion media, Kd's are ranged between 1.760 and 4.110 × 103 l mol−1. Thionine (with no methyl substitution) and azure A (with two methyl substitution) displayed slightly larger Kd values in microemulsion water pools compared to bulk water while other dyes recorded significant drop in Kd values. The influence of microemulsion media on the molecular interaction of dyes has been explained in terms of electrostatic and hydrophobic factors. The monomer and the dimer spectra are explained in terms of molecular exciton model and the optical absorption parameters of both the species are reported in bulk and confined media.