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

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 angstrom) 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.