Molecular aggregates of merocyanine 540 with different surfactant systems

Abstract

Merocyanine 540 (MC540) is a dye molecule that displays diverse photophysical features in varying environments. Micelle environments exert intriguing influences on the behavior of such molecules. This study’s primary objective is to examine the spectroscopic and thermodynamic consequences with different surfactants on the aggregation tendency of MC540. Interactions of MC540 with negatively charged sodium dodecyl sulphate (SDS), neutral triton X-100 (TX100) and positively charged hexadecyltrimethylammonium bromide (CTAB) surfactants were investigated by using molecular absorption spectroscopy. The interactions of MC540 with the SDS, CTAB, and TX100 under and above critical micelle concentration (CMC) were studied and H aggregate formation was observed under CMC. This H aggregate structure leaded to a shift towards monomer band above the CMC of SDS, TX100, CTAB according to the H aggregate-monomer equilibrium. Moreover, it was firstly observed that MC540 has trimer type aggregate structures as well with varying CTAB concentrations. In addition, by using temperature studies, thermodynamic function ΔH⁰dis values, dimer and trimer structures, were calculated as 6.10 kcal/mol, and 8.94 kcal/mol, respectively, and ΔS⁰dis values for dimer and trimer structures as −3.87 cal/Kmol, and −18.39 cal/Kmol, respectively. The calculated thermodynamic functions showed that disaggregation of aggregates is endothermic in nature and entropy is the driving force.