Role of manganese-based surfactant towards solubilization and photophysical properties of fluorescein

Abstract

Dye–surfactant interactions have been explored from various viewpoints in recent years, in the present work interactions between fluorescein dye and manganese-based, water-soluble surfactant for modulating photophysical properties of photosensitizer in a metal-containing microheterogeneous environment and for evaluating their role in solubilization have been evaluated. For these purposes, manganese (Mn) surfactant complexes were prepared in different ratios of metallic counter ions to numbers of hydrocarbon chains, that is, 1 : 1 and 1 : 2. The formulated complexes were further characterized by diverse techniques such as Fourier-transform infrared spectroscopy (FTIR), elemental analysis, thermogravimetric analysis, and nuclear magnetic resonance (NMR). Thermal stability of manganese surfactant complexes and kinetics of decomposition were investigated. The effect of metallic counter ions and temperature were evaluated on surface activity and aggregation of manganese surfactants, where the presence of metal ions lowered the critical micellization concentration and also affected the packing of adsorbed molecules at the air–solution interface. Our investigation further capitalized on the spectral sensitivity of fluorescein dye in the pre- and post-micellar system of manganese surfactant complexes. The influence of manganese surfactant complexes on the photophysics of fluorescein dye was thoroughly investigated using spectrofluorimetric parameters such as the Stern–Volmer constant, binding constant and anisotropy. NMR was used to locate the binding site of dye molecules in metallomicelles. Fluorescence quantum yield and singlet oxygen quantum yield were estimated using comparative methods, and increased fluorescence and singlet oxygen quantum yields were observed for dye on solubilization in metallomicelles as compared to conventional surfactants.