Rearrangement of Sb···Br Secondary Bonds Resulting in Reversible Transformation between Dimeric and Chain-Like Antimony Bromide Hybrid Materials: Tunability of Electron Self-Trapped Luminescence and Proton Conductivity

Single-crystal-to-single-crystal (SCSC) transformation materials are of great research interest because of their promising applications, among which multifunctional switching as next-generation intelligent materials in photoelectric devices is rare, and the corresponding mechanism remains unclear. Herein, we present two organic-inorganic hybrid antimony halides, namely (H₂dach)₂Sb₂Br₁₀·4H₂O (<b>1</b>) and (H₂dach)SbBr₅ (<b>2</b>) (dach = 1,2-diaminocyclohexane) and their reversible mutual SCSC transformation. <b>1</b> and <b>2</b> adopt zero-dimensional discrete butterfly-like [Sb₂Br₁₀]^4- dimers and one-dimensional infinite [SbBr₅]_<i>n</i>^2<i>n</i>- chains, respectively, possessing abundant Sb···Br secondary bonds due to the strong stereochemical activity of 5s² lone-pair electrons in Sb(III). Detailed structural analyses reveal that the reversible SCSC transformation is triggered by the rearrangement of Sb···Br secondary bonds, which enables the 25-time modulation of electron self-trapped photoluminescence with broadband orange emission. Humidity-dependent photoluminescence behavior of dehydrated <b>2</b> was also observed, which can be used to sense trace amounts of water. Furthermore, SCSC transformation via dehydration-rehydration could tailor hydrogen-bonding networks, resulting in switchable proton conductivity. The simulated kinetic mechanism of SCSC transformation by DFT is in agreement with the experimentally observed rearrangement of Sb···Br secondary bonds. This work demonstrates that the rearrangement of Sb···Br in hybrid halide systems is beneficial for elucidating dynamic transformation processes and promoting the development of multifunctional materials.