Steady state and time-resolved fluorescence spectroscopy of cinchonine dication in sodium dodecylsulphate micellar system

Abstract

This paper reports the influence of surface charge of the micelles on to the photophysical properties of a cinchonine dication (C2+) fluorophore in anionic, sodium dodecylsulphate (SDS), surfactant at premicellar, micellar and post-micellar concentrations in aqueous phase at room temperature. The magnitude of edge excitation red shift (EERS) in the fluorescence maximum of C2+ in bulk water solution is 1897 cm− 1 whereas, in the case of SDS it is observed to be 1984 cm− 1. The fluorescence decay curve of C2+ fits with multi exponential functions in the micellar system. The increase in lifetime of C2+ in SDS has been attributed to the increase in radiative rate due to the incorporation of C2+ at the micelle –water interface. The value of dynamic quenching constant determined is 16.9 M− 1. The location of the probe molecule in micellar systems has been justified by a variety of spectral parameters such as dielectric constant, ET (30), viscosity, EERS, average fluorescence decay time, radiative and non-radiative rate constants. All experimental results suggest that the C2+ molecule binds strongly with the SDS micelles and resides at micellar–water interface. The binding constant (Kb) calculated (3.85 × 105 M− 1) for C2+ in SDS revealed that the electrostatic forces mediate charge probe-micelle association.