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

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 K₁₁ = 5.92(7) × 10³ 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.