Preferential Molecular Encapsulation of an ICT Fluorescence Probe in the Supramolecular Cage of Cucurbit[7]uril and β‑Cyclodextrin: An Experimental and Theoretical Approach Anuva Samanta, † Nikhil Guchhait,* ,‡ and Subhash Chandra Bhattacharya* ,† † Department of Chemistry, Jadavpur University, Raja S. C. Mallick Road, Kolkata 700 032, India ‡ Department of Chemistry, University of Calcutta, 92, A. P. C. Road, Kolkata 700 009, India * S Supporting Information ABSTRACT: Supramolecular interaction between an intramolecular charge transfer (ICT) probe, N, N-dimethylaminonaphthyl-(acrylo)-nitrile (DMANAN), and two well-recognized macrocyclic hosts, cucurbit[7]uril (CB7) and β-cyclodextrin (β-CD), has been studied in aqueous medium by absorption, emission, time-resolved measurements, and 1 H NMR spectro- scopic methods. The changes in the profiles of the fluorescence spectra illustrate significant modifications in fluorescence intensity, decay time, and quantum yield upon confinement of probe within the hydrophobic cavity of the hosts. Using the Benesi−Hildebrand relationship, the stoichiometric ratio as well as the binding constant of the host−guest complexation has been estimated. The stable inclusion complexes of the probe with different hosts have been supported by DFT and ONIOM based quantum chemical calculations. These methods of measurement establish that the acceptor group of the probe resides inside the hydrophobic cavity of the macrocycle. The competitive binding of metal ions and cationic surfactants to CB7 has been excellently mapped with this guest fluorosensor. ■ INTRODUCTION Rigid molecular containers with different cavity size, capable of encapsulating small molecules, are of much interest because of their widespread applications in nanotechnology, separations, catalysis, nanoreactors, sensors, and drug delivery. 1−3 To this end, supramolecular chemists have judiciously designed and synthesized a wide variety of non-natural receptors, including cyclodextrins, crown ethers, calixarenes, and cyclophanes, and evaluated their recognition properties as drug carriers. Their primary aim is to enhance the solubility, stability, and bioavailability of drug molecules. 4−7 A new class of similar supramolecular hosts is the pumpkin-shaped cucurbit[n]urils (CBn), which are composed of n (5−10) glycoluril units linked by a pair of methylene groups (Scheme 1). The supramolecular hosts CBn have fairly rigid hydrophobic cores of different sizes with low polarity and polarizability. 8−10 Although Behrend 11 first prepared CB molecules in 1905, its structure was determined in 1981 by Mock and co-workers. 12 CBs have often educed comparisons with well-studied cyclodextrins (CDs) molecules. 13−15 The CB6, CB7, and CB8 hosts have comparable cavity volumes and sizes to those of α-CD, β-CD, and γ-CD, respectively. 16,17 However, the composition and binding properties of CBs are quite different from CDs. CDs are natural products generated by the action of the enzyme cyclodextrinase on starch, and these are composed of chiral glycopyranose units joined by acetal linkages. 13−15 On the other hand, CBs, as synthetic products, are prepared by the acid-catalyzed condensation of symmetric glycoluril repeating units with formaldehyde and consist of glycoluril monomers joined by pairs of methylene bridges. Both the cavity openings Received: August 6, 2014 Revised: October 22, 2014 Published: October 22, 2014 Scheme 1. Schematic Representation of the Structures of (a) DMANAN, (b) CB7, and (c) β-CD Article pubs.acs.org/JPCB © 2014 American Chemical Society 13279 dx.doi.org/10.1021/jp5079339 | J. Phys. Chem. B 2014, 118, 13279−13289