Modulated photophysics and rotational-relaxation dynamics of coumarin 153 in nonionic micelles: the role of headgroup size and tail length of the surfactants

Abstract

Here, the effect of variation in the headgroup size and the alkyl tail length of nonionic surfactants on the photophysics and rotational-relaxation dynamics of the laser dye coumarin 153 (C153) has been explored. The variation in the headgroup size, that is, poly(ethylene oxide) (PEO) chain length of the nonionic micellar systems, has been implemented using a variety of surfactants belonging to Triton X family, whereas surfactants from the Tween family provides an access to the variation of the tail length (alkyl chain) of the surfactants. Our spectroscopic study reveals a remarkable influence on the photophysics of C153 upon binding with the micelles. The strength of the dye-micelle binding interaction is found to be largely controlled by the variation of the headgroup size and the length of the tail of the surfactants. To this end, the dye-micelle binding interaction has been quantitatively assayed from emission studies and carefully interpreted based on the micellar hydration model. The estimation of the micropolarity of the dye binding site is further employed to corroborate this argument. Furthermore, all these line of arguments are effectively substantiated from time-resolved fluorescence experiments with particular emphasis on the modulation of rotational dynamics of the dye within the micellar micro-heterogeneous environments.