Rational Design of a Super-Alkali Compound with Reversible Photoluminescence.

The zero-dimensional (0D) (HO)(CHNS)BiCl: Sb single crystal is obtained by the cooling crystallization method. Surprisingly, this compound shows reversible photoluminescence (PL) upon HOCl removal and insertion. To be specific, the release of HOCl resulted in red-orange emission with a very low photoluminescence quantum yield (PLQY). While on the reuptake of it, a bright yellow emission with a nearly 10-fold increase of PLQY was observed. Density functional theory (DFT) calculations and temperature-dependent PL experiments reveal that significant [SbCl] octahedron distortion induced by guest (HOCl) removal at the ground state, especially at the excited state, is responsible for the disparate PL performance. Encouragingly, we also found that (CHNS)BiCl: Sb exhibits a fast response (<3 s) to dilute hydrochloric acid with naked-eye perceivable PL color changes, rendering it a potential sensing material for hydrochloric acid.