Solvent and rotational relaxation of coumarin-153 and coumarin-480 in ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) modified sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (NaAOT) micelle

Vishal Govind Rao, Chiranjib Banerjee, Sarthak Mandal, Surajit Ghosh, Nilmoni Sarkar

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Abstract

Understanding ion transport dynamics, structure of surfactant aggregates in ionic liquids or ionic liquid/water solutions are quite interesting and potentially important due to widespread applications of surfactant-based systems. In this manuscript we have investigated the effect of 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) addition on solvent and rotational relaxation of coumarin-153 (C-153) and coumarin-480 (C-480) in aqueous solution of sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (NaAOT) using steady state and picosecond time resolved fluorescence spectroscopy. The strong adsorption of the bmim+ at the interface and the role of the ionic liquid particularly the cation bmim+ in the modification of the interfacial geometry were probed by the analysis of decay parameters and the rotational relaxation parameters. Since the addition of the NaAOT in water-bmimBF4 mixture above critical micellar concentration (48 mM, obtained from observing pyrene fluorescence) causes strong adsorption of the ionic liquid particularly the cation bmim+, the average solvation time, particularly the slow component increases significantly. More importantly we have found the probe dependent solvation dynamics due to the different location of the probe molecules, C-153 and C-480. C-153 being hydrophobic in nature resides in the stern layer and the adsorption of the bmim+ at the interface modifies stern layer more effectively. So we have observed more pronounced change in solvation dynamics in case of C-153 compared to that in case of C-480. The fluorescence anisotropy decays of the probe molecules were found to be biexponential in nature. The anisotropy decay was interpreted by using a model which consists of the wobbling (rotational) and translational diffusion of the dye coupled with the rotational motion of the micelle as a whole.

Original languageEnglish (US)
Pages (from-to)371-378
Number of pages8
JournalSpectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
Volume102
DOIs
StatePublished - Feb 2013

Bibliographical note

Funding Information:
The work in this Letter is based on observations carried out at the European Southern Observatory (ESO) under program 075.C-0355(A). This program was part of a joint European initiative in support of the NASA Deep Impact mission to comet 9P/Tempel 1 by ground-based observations at La Silla and VLT Paranal. Some of the material presented herein is based on data obtained at the W. M. Keck Observatory, which immediately made its data available to the public after impact occurred on 2005 July 4. The W. M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to get observations from this mountain. J. M. is Research Director, and D. H. is Research Associate, at FNRS (Belgium).

Keywords

  • Amphiphile
  • Hydrophobicity
  • Ionic liquid
  • Rotational relaxation
  • Solvent relaxation

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