Steady-state fluorescence and photophysical properties of a ketocyanine dye in binary surfactant and polymer–surfactant mixture

Steady-state and time-resolved fluorescence studies have been done using a ketocyanine dye in heterogeneous media containing binary mixtures of sodium dodecyl sulphate (SDS) and triton X-100 (TX-100), and SDS+polyvinyl pyrrolidone (PVP). The dye molecules are found to distribute between core and interfacial region of the micelles. The band corresponding to the dye molecule in the core region exhibits red edge excitation shift. Study of lifetime in picosecond domain reveals that the de-excitation of the excited state of the dye via radiative pathway (kr) is independent of environment. The non-radiative decay constant (knr) on the other hand has been found to depend on the nature of environment, the core region being characterised by a faster decay rate. The slower decay rate in the interfacial region has been explained as due to hydrogen bonding interaction of the carbonyl group of the dye with protic solvents. Interesting variation of knr in the core region with surfactant composition has been observed which is explained in terms of surfactant–surfactant interaction in the micelles. Microviscosities at the micelle–water interface has been determined. For binary mixture of surfactants, the value of microviscosity has been found to deviate from ideality. An index of deviation from ideality has been proposed.