Complexation of sym-bis(benzimidazole)-2,2′-ethylene salts with cucurbit[6]uril derivatives: A potential axle molecule for pseudorotaxanes

Sym-bis(benzimidazole)-2,2′-ethylene cations act as a new axle template for threading cucurbit[6]uril derivatives on, forming [2]pseudorotaxane and [3]pseudorotaxane. These new complexes have been studied using 1H NMR, UV–vis absorption spectroscopy and X-ray analysis. Changes in the 1H NMR spectra indicate that the two types of pseudorotaxane can be formed by varying the host concentration. UV–vis absorption titration experiments at different pH values demonstrate that interesting pKa shifts of the bis-benzimidazole derivatives can be induced by the host–guest complexation. The associated constants were calculated to be 2.81 × 104 L/mol and 9.06 × 106 L/mol for the [2]pseudorotaxanes and [3]pseudorotaxanes, respectively. Furthermore, X-ray diffraction studies of the solid state structures provide unequivocal proof of the host concentration dependent pseudorotaxane, which is strongly in line with the evidences in solution.

Graphical abstractWe described here is that sym-bis(benzimidazole)-2,2′-ethylene cations act as a new axle template for threading cucurbit[6]uril derivatives on, forming [2]pseudorotaxane and [3]pseudorotaxane.Figure optionsDownload full-size imageDownload as PowerPoint slide