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Encapsulation of 2-(4′-N,N-dimethylamino)phenylimidazo[4,5-b]pyridine in β-cyclodextrin: effect on H-bond-induced intramolecular charge transfer emission

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Abstract

The effect of β-cyclodextrin (β-CD) inclusion complex formation on the hydrogen bond-induced intramolecular charge transfer (ICT) of 2-(4’-N,N-dimethylamino)phenylimidazo[4,5-b]pyridine (DMAPIP-b) has been examined by fluorescence excitation, emission and time-resolved fluorescence techniques. The study reveals that DMAPIP-b forms 1?:?1 inclusion complex with β-CD. The host -guest complex is formed by partial inclusion of DMAPIP-b,i.e. only the dimethylaminophenyl ring is encapsulated inside the core of the β-CD nanocavity. The imidazopyridine ring of the guest molecule resides outside CD cavity and forms H-bonds with the water molecules that are present near the rim and in the bulk phase. 1H NMR studies are used to confirm the inclusion complex. The H-bond of water with the pyridinenitrogen ensures the formation of the ICT state and both normal and ICT emissions are enhanced inside the β-CD cavity. Fluorescence lifetime measurements suggest that the formation of the ICT state from the locally excited state is irreversible. Dual emission is observed in the presence of β-CD at pH ~ 3.5, due to emission from monocations formed by the protonation of pyridine nitrogen (MC1) and imidazolenitrogen (MC2).

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  1. Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, 781039, India

    Nihar Dash, Francis A. S. Chipem & G. Krishnamoorthy

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  1. Nihar Dash
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  2. Francis A. S. Chipem
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  3. G. Krishnamoorthy
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Correspondence to G. Krishnamoorthy.

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† Electronic supplementary information (ESI) available: 1H NMR spectrum of DMAPIP-b in CDCl3; proton decoupled 1H NMR spectra of DMAPIP-b in CDCl3. See DOI: 10.1039/b9pp00023b

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Dash, N., Chipem, F.A.S. & Krishnamoorthy, G. Encapsulation of 2-(4′-N,N-dimethylamino)phenylimidazo[4,5-b]pyridine in β-cyclodextrin: effect on H-bond-induced intramolecular charge transfer emission. Photochem Photobiol Sci 8, 1708–1715 (2009). https://doi.org/10.1039/b9pp00023b

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