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Hydrogen Bond Sensitive Probe 5‑Methoxy-1-keto-1,2,3,4-tetrahydro Carbazole in the Microheterogeneity of Binary Mixtures and Reverse Micelles

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journal contribution
posted on 07.02.2013 by Manas Kumar Sarangi, Amrit Krishna Mitra, Chaitrali Sengupta, Sujay Ghosh, Suchandra Chakraborty, Chandan Saha, Samita Basu
The structure and dynamics of water under confinement differ drastically from its bulk behavior and show a considerable degree of inhomogeneity due to disruption in its hydrogen bonding (H-bonding) network. We attempt to probe such a microheterogeneous environment of reverse micelles (RMs) as well as binary mixtures of acetonitrile–water and ethanol–water by a H-bond sensitive probe 5-methoxy-1-keto-1,2,3,4-tetrahydro carbazole (MTC). Photophysical properties (quantum yield, lifetime, λmax) of MTC in the excited states are found to be extremely sensitive to the changes in the H-bonding of its immediate local environment. We observe huge Stoke’s shifts in the λmaxem of MTC with variation in the solvent environment, as we increase the polarity inside the nanopool of RMs and the mole fractions of water in the binary mixtures. We are able to effectively sense the subtle changes in the H-bonding network inside RMs with an increase in w0 and the formation of self-aggregated microclusters inside the binary mixtures, by measuring the photophysical variations in steady state and time-resolved fluorescence of MTC. An iso-emissive point in the time-resolved area normalized spectra of MTC inside RMs suggests the presence of two distinct emissive species of MTC, (a) MTC* and (b) H-bonded MTC, h-MTC*, which are expected to be predominant in nonaqueous and aqueous media, respectively. The variations in the nature and type of the H-bonding in such self-assemblies and clusters with changes in aqueous environment are very well characterized by the photophysics of two isomers of MTC.