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Issue 7, 2013
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Cucurbit[5]uril–metal complex-induced room-temperature phosphorescence of α-naphthol and β-naphthol

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Similar to the larger members of the cucurbituril family, such as cucurbit[8]uril (Q[8]), the smallest member, cucurbit[5]uril (Q[5]), can also induce room-temperature phosphorescence (RTP) of α-naphthol (1) and β-naphthol (2). The relationship between the RTP intensity of 1 and 2 and the concentration of Q[5] or Q[8] suggests that the mechanism underlying the Q[5] complex-induced RTP is different from that of the Q[8]-induced RTP for these luminophores. The crystal structures of 1–Q[5]–KI, 2–Q[5]–KI, 1–Q[5]–TlNO3, and 2–Q[5]–TlNO3 systems show that in each case Q[5] and the respective metal ions, K+ or Tl+, form infinite ⋯Q[5]–M+–Q[5]–M+⋯ chains that surround the luminophores. Although these tube- or wall-like structures are likely destroyed in solution, the key interaction between the convex-shaped outer walls of Q[5] and the plane of the aromatic naphthols, via π⋯π stacking and C–H⋯π interactions, is postulated to be essentially maintained leading to a microenvironment that holds the luminophore and the heavy atom perturber together; such a model is supported by the observed Q[5] complex-induced RTP of the above naphthols. With respect to this, a high Q[5]/luminophore concentration was employed in an endeavour to promote the formation of π⋯π stacking and C–H⋯π interactions similar to those observed in the crystal structures of the 1– or 2–Q[5]–K+ and –Tl+ systems. In keeping with the proposed model, the RTP of each system is quenched when Q[5] is replaced by the alkyl-substituted Q[5] derivatives, decamethylQ[5] and pentacyclohexanoQ[5]. This is in agreement with the substituent groups on the surface of the metal-bond Q[5] obstructing the naphthol molecule from accessing the convex glycouril backbone of Q[5].

Graphical abstract: Cucurbit[5]uril–metal complex-induced room-temperature phosphorescence of α-naphthol and β-naphthol

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Publication details

The article was received on 31 Aug 2012, accepted on 15 Nov 2012 and first published on 15 Nov 2012

Article type: Paper
DOI: 10.1039/C2DT32002A
Citation: Dalton Trans., 2013,42, 2608-2615
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    Cucurbit[5]uril–metal complex-induced room-temperature phosphorescence of α-naphthol and β-naphthol

    Z. Gao, X. Feng, L. Mu, X. Ni, L. Liang, S. Xue, Z. Tao, X. Zeng, B. E. Chapman, P. W. Kuchel, L. F. Lindoy and G. Wei, Dalton Trans., 2013, 42, 2608
    DOI: 10.1039/C2DT32002A

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