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

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Title Unique Effects of Aerosol OT Lamellar Structures on the Dynamics of Guest Molecules
 
Creator DE, D
DATTA, A
 
Subject DOUBLE-PROTON-TRANSFER
SOLVATION DYNAMICS
SUPRAMOLECULAR ASSEMBLIES
RESOLVED FLUORESCENCE
REVERSE MICELLES
COUMARIN 480
WATER
SOLVENT
2,2-BIPYRIDINE-3,3-DIOL
N,N-DIMETHYLACRYLAMIDE
 
Description The behavior of lamellar structures of Aerosol OT (AOT) as hosts, vis-a-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.
 
Publisher AMER CHEMICAL SOC
 
Date 2014-10-16T14:51:24Z
2014-10-16T14:51:24Z
2013
 
Type Article
 
Identifier LANGMUIR, 29(25)7709-7714
0743-7463
1520-5827
http://dx.doi.org/10.1021/la401564b
http://dspace.library.iitb.ac.in/jspui/handle/100/15830
 
Language en