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 (λmaxem = 485 nm, ΦF = 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.