Driving π-plane to π-bowl through lateral coordination at room temperature

Abstract

A series of hetero polycycles (5a-6b) are created through the hybridization of the bowl-shaped trichalcogenasumanenes and planar triazacoronene. Among them, 6a and 6b bear the 2,2′-bipyridine (bpy) ligand in the lateral direction. The crystallographic analyses show that 6a and 6b possess planar cores, whereas they are driven to bowl-shaped (bowl depth, 0.38–0.50 Å) via chelation of Zn²⁺ by the bpy unit at room temperature (RT). This is caused by the formation of a five-membered ring upon coordination with Zn²⁺. The coordination of Zn²⁺ also brings distinct variation of the optical properties, i.e., the crystals of 6a and 6a[ZnCl₂] respectively show green and red fluorescence. Moreover, 5a-6b exhibit a reversible color change and a fluorescence OFF/ON response upon acidification and neutralization. Owing to the multiple protonation process, 6a and 6b display a gradient color change from yellow to magenta, violet, and blue as the amount of acid increases. These new hetero polycycles (5a-6b) have potential applications as chemosensors and/or switches.