The host–guest complexations of HMeQ[7] with a series of alkyldiammonium ions and alkyldiamines have been investigated, indicating that the driving forces strongly depend on the features of the guests.

Environmentally benign methods for gold recovery and detection are highly desirable for a sustainable future. Herein, we demonstrate a selective recovery and detection strategy of gold with cucurbit­[n]­urils (Q­[n = 5–7]) by means of outer-surface interactions. Tetrachloroaurate anion ([AuCl4]−) is able to be rapidly precipitated with Q­[n] in forms of supramolecular adducts. X-ray crystallography of four Q­[n = 5–7]·[AuCl4]− complexes reveal that strong outer-surface interactions between Q­[n = 5–7] and [AuCl4]− are the major driving force for the formation of Q­[n = 5–7]·[AuCl4]− complexes. Impressively, each Q[6] macrocycle is surrounded by 12 [AuCl4]− anions. Each of these 12 [AuCl4]− anions is connected to four adjacent [AuCl4]− anions, leading to the formation of a three-dimensional supramolecular framework with tubular channels. In addition, we found an interesting inclusion complex [Au­(OH2)4]3+⊂Q­[7] in the Q[7]·[AuCl4]− complex, which is the first example of hydrated metal cation encapsulated inside the cavity of Q­[n]. Spectroscopic data suggest that Q­[n = 5–7] possess a high affinity and selectivity for [AuCl4]− even in the presence of other transition-metal ions. Q­[n] modified electrodes are found to be an effective material for the detection of trace gold in dilute solutions.

According to a simple guest-replacement fluorescence turn-on mechanism, we constructed a fluorescent probe system based on cucurbit[10]­uril (Q[10]) and protonated acridine (AD) to detect the pesticide dodine (DD). Formation of a homoternary inclusion complex AD 2@Q­[10] in both aqueous solution and solid state was studied by means of 1H NMR spectroscopy and X-ray crystallography. Although AD can emit strong fluorescence in aqueous solution, the homoternary inclusion complex AD 2@Q­[10] does not exhibit any fluorescence. Upon the addition of the pesticide DD into the aqueous solution of AD 2@Q­[10], the AD molecules in the Q[10] cavity are displaced by the pesticide DD, and strong fluorescence recovers. The fluorescent probe system based on Q[10] and AD provided a wide determination of DD from 0 to 4.0 × 10–5 mol·L–1 with a low limit of detection of 1.827 × 10–6 mol·L–1. The guest-replacement fluorescence turn-on mechanism is also confirmed by 1H NMR spectroscopy. Further, the fluorescent probe can directly detect DD residues in real agricultural products, and obvious fluorescence signal was observed under UV irradiation.

β-Cyclodextrins (β-CDs) are shown to form 1:1 and 2:1 host−guest inclusion complexes with two carboxyphenyl viologens, 1-(4-carboxyphenyl)-4,4′-bipyridinium chloride (1 + • Cl − ) and 1,1′-bis(4-carboxyphenyl)-4,4′-bipyridinium dichloride (2 2+ •Cl 2 − ), in an aqueous solution. The solid-state supramolecular host−guest inclusion complexes 1 + @β-CD and 2 2+ @β-CD 2 demonstrate excellent photochromic properties. The results of the electron-spin resonance (ESR) spectroscopy suggest that their photochromic behaviors are caused by the generation of free radicals (V •+ ). The energy-minimized structure and the calculated reorientation energy of the inclusion complex 1 + @β-CD support the electron transfer from the host β-CD to the guest 1 + . The practical applications of the inclusion complex 1 + @β-CD as erasable inkless printing media and an anticounterfeiting material were also studied. The present study provides a supramolecular method for the construction of photochromic materials.

No abstract