Explicit spectral response of an intramolecular charge transfer molecule within microheterogeneous micellar environments

Abstract

Photophysical properties of a potent intramolecular charge transfer probe viz., 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester (DPDAME) have been investigated in aqueous micellar environments using spectroscopic techniques. The intramolecular charge transfer (ICT) fluorescence of DPDAME is found to display remarkable hypsochromic shift coupled with intensity enhancement within the microheterogeneous micellar environments. This is also associated with discernible increase in fluorescence anisotropy whereby indicating the impartation of considerable motional restrictions on the fluorophore within the micellar systems. The fluorescence anisotropy results are also processed to delve into an estimate of the microviscosity of the probe environment at the binding site on the micellar aggregates. Quantitative evaluation of the probe–micelle binding strength has been achieved from fluorescence data in terms of binding constant and free energy change of the interaction process. The extensive polarity-sensitive fluorescence behavior of DPDAME has been exploited to cast light on assessing the micropolarity at the interaction site of the probe within the micelles. This information has in turn been efficiently employed as the actuating avenue to argue on complex issues like probable location, distribution and orientation of the probe within the micellar aggregates. The pattern of variation of emission intensity of DPDAME as a function of surfactant concentrations is found to reveal the existence of multiple critical micellar concentration (CMC). Overall, the present results have been argued to reflect the commendable efficiency of DPDAME to function as a prospective molecular reporter for complex microheterogeneous micellar environments.