Spectroscopically probing the effects of Holmium(III) based complex counterion on the dye-cationic surfactant interactions

Interactions between dyes and surfactants is a well-established research area. It is important to interpret the missing links related to the differences between the relatively newer surfactant entrants with respect to their modified counterions and their conventional counterparts. In this research, we explored and compared the interactions of a commercial cationic surfactant dodecyltrimethylammonium bromide (DTAB) and a modified surfactant having optically active counterion, trichlromonobromoholminate, with model dyes methyl orange (MO) and eriochrome black T (EBT). The effect of a cationic surfactant DTAB and the same surfactant with modified counterion dodecyltrimethylammonium tricholomonobromoholminate (DTAH) on the electronic properties of model azo dyes MO and EBT were studied in the premicellar and postmicellar concentrations of surfactants. UV-Visible (UV-Vis) and steady state fluorescence spectroscopies (SSF) were employed to probe the interactions between dyes and surfactants. The binary associations were rationalized by quantitative mathematical models including benesi-hildebrand and stern volmer equations. The variations in the dye electronic properties caused by the two counterions were estimated by various parameters including, binding constants, k(a) and k(b), binding affinity 'a' and Gibbs free energy of binding Delta G(b). The results show that extent of binding of modified surfactant DTAH with dye is reduced when compared to conventional cationic surfactant DTAB. Moreover, the study sheds light on the impact of inorganic counterion on solubilization of dyes and possible locus of dye as well as counterion in the modified micellar and pre-miceller systems. [HoCl3Br](-1) counterion clearly alter the optical response of MO and EBT dyes in the presence of surfactant system due to the formation of complex by Holmium(III) and azo dyes.