Unique Effects of Aerosol OT Lamellar Structures on the Dynamics of Guest Molecules

Abstract

The behavior of lamellar structures of Aerosol OT (AOT) as hosts, vis-à-vis the flexible normal micelles and rigid nanochannels of Nafion membranes, has been investigated with two different fluorophores, [2,2'-bipyridyl]-3,3'-diol (BP(OH)2) and coumarin 102 (C102). Surprisingly, for BP(OH)2, a rise time is observed at intermediate emission wavelengths and not in the red edge of the fluorescence spectrum. A shoulder at 525 nm is observed in time resolved emission spectra (TRES) at initial times of BP(OH)2 in AOT lamellar structures. This feature is the signature of the monoketo (MK) tautomer, observed for the first time in a microheterogeneous medium. Also, the usually ultrafast single proton transfer in BP(OH)2 is retarded to an considerable extent in lamellar structures. The potential of this medium in promoting unusual intermediates is thus highlighted. This property may be ascribed to the rigidity of lamellar structures, compared to hosts such as regular micelles. However, studies using another fluorophore, coumarin 102 (C102), brings out the fact that these structures are significantly different from the rigid host, Nafion, as well. The absence of excited state proton transfer (ESPT) in this molecule in AOT lamellar structures indicates that it is not protonated, unlike in Nafion. Thus, the interfacial pH of lamellar structures is found to be significantly greater than that of Nafion nanochannels. From the time dependent Stokes shift (TDSS) of the emission spectra of C102, the relaxation time (0.85 ns) of interfacial water in lamellar structures is found to be an order of magnitude faster than that observed in Nafion nanochannels, in which H3O(+) ions have been substituted by different cations. Hence, this study demonstrates that AOT lamellar structures are rather unique hosts and that they behave very differently from conventional rigid and flexible hosts such as normal micelles and Nafion, respectively.

Anisotropic dynamics of guest molecules in aerosol OT lamellar structures

“…18,19 However, only five fluorescence spectroscopic studies have been performed on these lamellar structures, to the best of our knowledge. 16,[20][21][22][23] Among these studies, the two that are most closely related to the present one are by Verma et al 16 and ourselves. 22 In the study of Verma et al, solvation dynamics in the lamellar structures has been reported, using coumarin 500.…”

“…This property enables the imaging of these structures using cross polarization optical microscopy (POM). 16,20,21,22,23 4 Among these studies, the two that are most closely related to the present one are by Verma et al 16 and ourselves. 16 Attempts have been made in recent times aiming the elucidation of these aspects and the multimodal relaxation dynamics of both the free and bound water molecules found at the interfaces of these lamellar aggregates using a variety of techniques like X-ray diffraction, 12 infrared spectroscopy, 12, 13, 17 NMR and differential calorimetry.…”

Surfactant-assisted hydrothermally synthesized MoS 2 samples with controllable morphologies and structures for anthracene hydrogenation

“…P123, as a common triblock copolymer, has a central hydrophobic chain and two hydrophilic chains and is facile to assemble into "lamellar" micelles because it is weakly hydrophobic [29]. It is easy for AOT to form lamellar micelles owing to the steric hindrance of its wedge-like structures [30]. Second, molybdate ions (Mo7O24 6− ) are easily adsorbed on the outer surfaces of these micelles via electrostatic interactions, as shown in step (II).…”

Effect of Microheterogeneity of Different Aqueous Binary Mixtures on the Proton Transfer Dynamics of [2,2′-Bipyridyl]-3,3′-diol: A Femtosecond Fluorescence Upconversion Study

“…Therefore, BP­(OH) 2 should not show any solvation dynamics. Moreover, Datta and co-workers have revealed that BP­(OH) 2 is not a solvation probe as the major band in the time-resolved emission spectra generated using the fitted parameters does not undergo a very prominent shift. Therefore, the solvation dynamics is not contributing to our spectral dynamics.…”