Effect of alkyl chain length and size of the headgroups of the surfactant on solvent and rotational relaxation of Coumarin 480 in micelles and mixed micelles

Abstract

The effect of alkyl chain length and size of the headgroups of the surfactant on the solvation dynamics and rotational relaxation of Coumarin 480 (C-480) has been investigated using dynamic Stokes' shift of C-480 in different types of alkyltrimethylammonium bromide micelles and mixed micelles. The rotational relaxation time increases with increase in alkyl chain length of the surfactant. The increase in the number of alkyl chains of the surfactant leads to the more close packed micelles, hence the microviscosity of the micelles increases and consequently rotational relaxation time increases. Solvation time also increases due to the increase in number of alkyl chains of the surfactant. The change in solvation and rotational relaxation time is more prominent in micelles compared to mixed micelles. The solvation and rotational relaxation time also increase with the increase in size of the headgroup of the surfactant.

Photophysics and rotational relaxation dynamics of a β-carboline based fluorophore in cationic alkyltrimethylammonium bromide micelles

“…Despite the fact that the E T (30) values around the fluorophore in the micelles studied do not differ very much, there is a gradual decrease in the value with an increase in the hydrocarbon chain length of the cationic surfactants form DTAB to CTAB through TTAB. Chakrabarty et al, in one of their works, reported very similar micropolarities around a coumarin derivative in nTAB micelles and reverse micelles [19]. The micropolarity values in the three nTAB micellar systems estimated from the present study are close to our earlier reported values where we constructed the calibration curve from the ratio of fluorescence intensities of the two prototropic forms of the proton transfer probe norharmane (NHM) [7].…”

“…Rotational diffusion of two ionic lipophilic fluorophores in alcohol and in SDS, CTAB, and TX-100 micellar environments was reported by Quitevis et al and the study has presented a detailed picture of the structural and dynamical aspects of the probes in micelle-water interfaces [22]. Study of the effect of hydrophobic chain length of surfactants on the dynamical behavior of a fluorophore was started rather recently [19][20][21]. Chakrabarty et al have reported the effect of varying chain length as well as head group of cationic surfactants on the rotational relaxation of coumarin 480 in micellar and mixed micellar environments [19].…”

“…5 reveals that the degree of rigidity imposed on the probe in these micellar media follows the order DTAB < TTAB < CTAB. These observations can be explained either from the consideration of the compactness of the micelles and water penetration through the micelles [7,19] or from the differential degrees of binding efficiencies of the probe with the nTAB micellar systems or both.…”

“…Study of the effect of hydrophobic chain length of surfactants on the dynamical behavior of a fluorophore was started rather recently [19][20][21]. Chakrabarty et al have reported the effect of varying chain length as well as head group of cationic surfactants on the rotational relaxation of coumarin 480 in micellar and mixed micellar environments [19]. Orientational relaxation studies of two biologically important dyes in alkyltrimethylammonium bromide (nTAB) and their chloride analogs (nTAC) have been studied by Fayer's group and they have determined the partition coefficients of the dyes that are distributed in two different domains of the micelles [20].…”

“…Dynamic behavior includes the rotational and/or tumbling motion of the bound fluorophore within the microheterogeneous environments on the picosecond/nanosecond time scale [3,19]. Development of pico-and femtosecond lasers has enabled the researchers to directly probe into the ultrafast relaxation processes in micellar environments by time-resolved fluorescence depolarization techniques [8,14,[19][20][21]. Dutt characterized various components of rotational motion of two structurally similar dyes in Triton X-100 (TX-100) micelle, where the growth of the micelle was induced by the addition of sodium chloride [3].…”