Feeding a Molecular Squid: A Pliable Nanocarbon Receptor for Electron-Poor Aromatics

Abstract

A hybrid nanocarbon receptor consisting of a calix[4]arene and a bent oligophenylene loop (“molecular squid”), was obtained in an efficient, scalable synthesis. The system contains an electron-rich cavity with an adaptable shape, which can serve as a host for electron deficient guests, such as diquat, 10-methylacridinium, and anthraquinone. The new receptor forms inclusion complexes in the solid state and in solution, showing a dependence of the observed binding strength on the shape of the guest species and its charge. The interaction with the methylacridinium cation in solution was interpreted in terms of a 2:1 binding model, with K 11 = 5.92(7) × 10 3 M –1 . The solid receptor is porous to gases and vapors, yielding an uptake of ca. 4 mmol/g for methanol at 293 K. In solution, the receptor shows cyan fluorescence (λ max em = 485 nm, Φ F = 33%), which is partly quenched upon binding of guests. Methylacridinium and anthraquinone adducts show red-shifted emission in the solid state, attributable to the charge-transfer character of these inclusion complexes.

N‐Substituted Acridinium as a Multi‐Responsive Recognition Unit in Supramolecular Chemistry

“…This color change was the result of the increased charge transfer from the phenolate to the acridinium moiety in 36 2 + (Figure 13b). Upon changing the cation of the base to less coordinating ions (Na + , K + , (CH 3 CH 2 ) 4 N + , Cs + ), a change of the spectral properties was observed with the appearance of a new species (λ max = 490 nm) attributed to the quinoid form (37). In all cases, slow conversion of the quinoidic calix [4]arene to the corresponding bis-acridane receptor (35) was achieved (λ max = nm).…”

“…M. Stępień and coworkers have functionalized a calix[4]arene with a oligophenylene loop ( 27 ) which delimits a flexible cavity (Figure 10a) [37] . Followed by NMR experiments, titration studies in CD 2 Cl 2 revealed a 1 : 1 host‐guest complex between Ac + and the oligophenylene loop through π‐π interactions (log K =3.77, Figure 10b).…”

“… Functionalized calix[4]arene with a bent oligophenylene loop ( 27 ). a) X‐ray crystal structure and b) π‐π interactions with Ac + with the corresponding binding constant (log K ) in CD 2 Cl 2 [37] …”

“…a) X-ray crystal structure and b) π-π interactions with Ac + with the corresponding binding constant (log K) in CD 2 Cl 2 . [37] cavity. Based on these results, the receptor was envisaged as a selective chromoionic indicator.…”

Supramolekulare Bindungstaschen in [n]Cyclo‐2,7‐pyrenylenen

“…Die Einbindung solcher Fragmente ermöglicht Untersuchungen neuer Funktionalitäten und optoelektronischer Eigenschaften dieser makrozyklischen Substanzklasse [13–17] . Zudem konnten durch diese methodischen Arbeiten neue geometrische Formen vom Makrozyklus bis hin zum molekularen Käfig erschlossen werden [18–21] . Während poröse molekulare Käfige intrinsisch ein Gastbindungsverhalten aufweisen, sind CPPs und verwandte gespannte Kohlenstoffmakrozyklen nur moderate supramolekulare Wirte, die sich meist auf die Bindung von Fulleren‐Gästen beschränken [22–27] .…”