Role of Dual Nature of Ionic Liquid in Solvation Dynamics and Rotational Diffusion in Mixed Micelles: A Time‐Resolved Fluorescence and Fluorescence Anisotropy Study

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The present work demonstrates the role of the dual nature of an ionic liquid, 1‐dodecyl‐3‐methylimidazolium bromide (C 12 mimBr), in the solvation dynamics and rotational diffusion of Coumarin 153 (C‐153) in the aqueous mixed micellar solutions of three cationic gemini surfactants, 12‐ s ‐12,2Br − (where s = 4, 6 and 8) using different spectroscopic and light scattering techniques. Ionic liquid within the micelles controls the weightages of solvation components. In pure micelles of a gemini surfactant, the fast and slow solvation components are major and minor, respectively, which vary based on the concentration of the ionic liquid. The effective solvation rate enhances with increasing concentration of C 12 mimBr. Dual nature of C 12 mimBr governs the size of mixed micelles. Thus the associated time constant for rotational motion also alters accordingly. In micelle, lateral diffusion coefficient ( D L ) value enhances with its increasing size due to mixed micelle's increased porosity. Gemini spacer chain length effect is also discussed.