Lead-Free Hybrid Metal Halides with a Green-Emissive [MnBr 4 ] Unit as a Selective Turn-On Fluorescent Sensor for Acetone

Organic–inorganic hybrid metal halides with zero-dimensional (0D) structure has emerged as a new class of light-emitting materials. Herein, a new lead-free compound (C 9 NH 20 ) 2 MnBr 4 has been discovered and a temperature-dependent phase transition has been identified for two phases (space group P 2 1 / c and C 2/ c ) in which individual [MnBr 4 ] 2– anions connect with organic cations, (C 9 NH 20 + ) (1-buty-1-methylpyrrolidinium + ), forming periodic structure with 0D blocks. A green emission band, peaking at 528 nm with a high photoluminescence quantum efficiency (PLQE) of 81.08%, has been observed at room temperature, which is originated from the 4 T 1 (G) to 6 A 1 transition of tetrahedrally coordinated Mn 2+ ions, as also elaborated by density functional theory calculation. Accordingly, a fast, switchable, and highly selective fluorescent sensor platform for different organic solvents based on the luminescence of (C 9 NH 20 ) 2 MnBr 4 has been developed. We believe that the hybrid metal halides with high PLQE and the exploration of these as a fluorescence sensor will expand the applications scope of bulk 0D materials for future development.