Multiple photoluminescence from pyrene-fused hexaarylbenzenes with aggregation enhanced emission features

Multiple photoluminescence, involved in monomer emission, excimer emission and charge transfer emission origin from new pyrene-fused hexaarylbenzenes (HAB) compounds were observed, which were designed and synthesized (in high yield) via the Diels-Alder reaction of bis(2-tert-butylpyren-6-yl)acetylene and tetraphenylcyclopentadienone. Although the distinction of between two molecules arises only from the geometrical position of one of the pyrenes, the NMR spectra, the crystal packing and the physicochemical properties of these pyrene-based HAB hybrids are distinctly different both in their solution state and in aggregation-state. The X-ray diffraction analysis clearly indicated that the pyrene moieties in this system would form different crystal packing in crystal state that can induce a fantastic multiple photoluminescence phenomenon

Host–guest interaction of hemicucurbiturils with phenazine hydrochloride salt

<div><p>The host–guest interactions between phenazine hydrochloride salt (PheH⁺) and hemicucurbit[<i>n</i>]uril (<i>n</i> = 6 or 12) (HemiQ[6 or 12]) have been studied by ¹H NMR, UV–vis, IR, mass spectrometry (MS) and quantum chemistry. In ¹H NMR spectra, the broadening of proton resonances of the hosts suggests the interactions of PheH⁺ with HemiQs. The quantitative stabilities of the host–guest systems have been obtained by UV–vis titration experiments, that is, the stoichiometric interactions of PheH⁺ with HemiQ[6] have been observed with an association constant of <i>K</i>_a = (2.5 ± 1.2) × 10⁶ L mol^− 1, while the 2:1 ratio complexes of PheH⁺ with HemiQ[12] are formed with stepwise association constants of <i>K</i>₁ = (9.2 ± 2.8) × 10⁴ L mol^− 1 and <i>K</i>₂ = (6.4 ± 0.9) × 10⁵ L mol^− 1, respectively, which induce a total association constant of <i>K</i>_a = 5.9 × 10¹⁰ L² mol^− 2. Both the 1:1 and 2:1 complexes have been detected by MS. Quantum chemistry calculations have been used to understand the static structures and thermodynamic stabilities of the supramolecular assemblies.</p></div

Cucurbit[7]uril-improved recognition by a fluorescent sensor for cadmium and zinc cations

<p>The host–guest interaction of cucurbit[7]uril (Q[7]) with the new fluorescent sensor guest molecule (<b>BIBPAH</b>^<b>+</b>), formed by alkylation of the secondary amine site in <i>N,N</i>-bis(2-pyridylmethyl)amine with 2-(bromomethyl)benzimidazole, was investigated by fluorescence and ¹H NMR spectroscopy. The results indicate the formation of an inclusion complex in a 1:1 ratio with an association constant of <i>K</i>_a = (2.9 ± 0.7) × 10⁵ L ∙ mol⁻¹. There is minimal difference in the fluorescence intensities upon the introduction of each of Mn²⁺, Ni²⁺, Co²⁺, Cr³⁺, Ho³⁺ and Lu³⁺. However, the emission was slightly quenched on the addition of Cu²⁺ or Fe³⁺ whether Q[7] is present or not. Further investigation showed that encapsulation of <b>BIBPAH</b>^<b>+</b> in Q[7] improves Cd²⁺ and Zn²⁺ recognition by enhancing the fluorescence intensity, leading to an improvement in the limits of detection. In contrast, comparative parallel experiments in which Cu²⁺, Mn²⁺, Ni²⁺, Co²⁺, Fe³⁺, Cr³⁺, Ho³⁺ or Lu³⁺ were substituted for Zn²⁺ or Cd²⁺ resulted in minimal changes in the fluorescence that occurs for the corresponding metal-free system. The natures of the encapsulated Zn²⁺ and Cd²⁺ complexes have been investigated using fluorescence and ¹H NMR spectroscopy as well as by quantum chemistry.</p> <p>The selectivity of a fluorescent sensor for Cd²⁺ and Zn²⁺ was improved by its encapsulation within the cavity of cucurbit[7]uril.</p

Mono- and Dihydroxylated Symmetrical Octamethylcucurbiturils and Allylated Derivatives

Mono- and dihydroxylated symmetrical octa­meth­yl­cu­cur­bit­[6]­urils {(OH)­OMeQ[6] and (OH)₂OMeQ­[6]} were prepared using a photochemical method to introduce limited alcohol group(s) directly to the parent symmetrical octamethylcucurbit[6]­uril (OMeQ[6]), and the resulting compounds were verified by ¹H NMR, Xevo Q-TOF MS, and X-ray crystallography. Further chemical modification of mono- and dihydroxylated OMeQ[6] was also performed

A Hemimethyl-Substituted Cucurbit[7]uril Derived from 3α-Methyl-glycoluril

A novel hemimethyl-substituted cucurbit[7]­uril (HMeQ[7]) derived from 3α-methyl-glycoluril has been prepared. HMeQ[7] is readily soluble in both water and dimethyl sulfoxide (DMSO) and displays not only host–guest interaction properties similar to those of the normal cucurbit[7]­uril but also unusual properties in DMSO