Chalcogenoviologen Enhanced Host–Guest Recognition

In the field of supramolecular chemistry, cyclophanes with novel properties are highly sought after since they can be tailored to fulfill specific tasks. In this article, we incorporate chalcogenoviologen-based units into tetracationic cyclophanes, resulting in enhanced host–guest recognition. The cyclophanes can be tuned through the addition of chalcogen bridging atoms—S, Se, and Te—which enhance their rigidity, regulate bond rotation and introduce additional steric bulk. Three cyclophanes containing chalcogen bridging atoms were synthesized and characterized in both the solution and solid states. The energy barriers for their interconversion between syn- and anti-conformations in solution were found to be correlated with chalcogen atom size. The photophysical properties of the cyclophanes are strongly dependent on the chalcogen atomic number, with intersystem crossing rates increasing from S to Se to Te. UV–vis-NIR spectroscopic and fluorometric titrations revealed that the chalcogenoviologen-based cyclophanes exhibit significantly stronger binding with electron-rich guests compared to the well-known, unsubstituted cyclobis(paraquat-p-phenylene). This enhancement in binding can be attributed to restricted rotation within the chalcogenoviologen units. This research provides insight into the rational design and tailored synthesis of cationic cyclophanes.