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Issue 32, 2017
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Cyclodextrin-assisted modulation of the photophysical properties and acidity constant of pyrene-armed calix[4]arene

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Abstract

The supramolecular interaction of cyclodextrin homologues with a pyrene-armed calixarene has been investigated. p-tert-Butylcalix[4]arene-di-4-(pyren-1-yl)butanoic acid (PCX4) has been synthesized and characterized by 1H NMR, FT-IR and mass spectrometry. The modulation in the photophysical properties, especially the monomer and excimer emission behaviour of the pyrene group in PCX4 with β-cyclodextrin (β-CD) and γ-cyclodextrin (γ-CD), has been explored in aqueous solutions by using optical absorption, steady-state and time-resolved fluorescence measurements. Steady-state fluorescence studies illustrate that upon gradual addition of γ-CD to the PCX4 solution, initially there is a decrease in the monomer emission (at 378, 398 and 420 nm) along with the appearance of weak excimer emission at 482 nm. Beyond a particular concentration of γ-CD (>1.2 mM), PCX4 shows strong excimer emission along with an increase in the monomer emission, indicating two types of interaction modes between PCX4 and γ-CD. Fluorescence anisotropy measurements confirm intramolecular excimer formation with a lower concentration of γ-CD, whereas it predominantly becomes an intermolecular excimer beyond 1.2 mM of γ-CD. On the other hand, the monomer emission of the pyrene group of PCX4 increases in the presence of β-cyclodextrin having lower cavity sizes due to the formation of a 1 : 1 complex. For the first time, the intrinsic fluorescence from the pyrene moiety of PCX4 is employed to determine the pKa value of PCX4 and it is ∼6.1. The cyclodextrin-encapsulated PCX4 brings a 1.2 unit downward pKa shift. Along with the pH-responsive interconversion of monomer to excimer emission of γ-CD complexed PCX4, this system can find applications in ratiometric sensing and optical supramolecular pH-sensors.

Graphical abstract: Cyclodextrin-assisted modulation of the photophysical properties and acidity constant of pyrene-armed calix[4]arene

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Publication details

The article was received on 24 Mar 2017, accepted on 24 Jul 2017 and first published on 25 Jul 2017


Article type: Paper
DOI: 10.1039/C7CP01894K
Citation: Phys. Chem. Chem. Phys., 2017,19, 21382-21389
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    Cyclodextrin-assisted modulation of the photophysical properties and acidity constant of pyrene-armed calix[4]arene

    V. S. Kalyani, D. D. Malkhede and J. Mohanty, Phys. Chem. Chem. Phys., 2017, 19, 21382
    DOI: 10.1039/C7CP01894K

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