Herein, anew mechanism, namely,crystalline phase recognition (CPR), is proposed for the single-crystal-to-singlecrystal (SCSC) transition of metal halides.C hiral b-[Bmmim] 2 SbCl 5 (Bmmim = 1-butyl-2,3-methylimidazolium) can recognizea chiral a- [Bmmim] 2 SbCl 5 on the basis of akey-lock feature through intercontact of their single crystals, resulting in ad omino phase transition (DPT). The concomitant photoluminescence (PL) switching enables observation of the DPT in situ. The liquid eutectic interface,s tress-strain transfer,a nd feasible thermodynamics are key issues for the CPR. DFT calculations and PL measurements revealed that the optical absorption and emission of the isomers mainly originate from [SbCl 5 ] 2À anions.T he structural effects (e.g., supramolecular interactions and [SbCl 5 ] 2À distortion) on the optical emission are clarified. As an ovel type of stimuli response,t he CPR-induced DPT and luminescence switching exhibit potential for application in advanced time-resolved information encryption.

Zero-dimensional (0D) metal halides with solid-state luminescence switching (SSLS) have attracted attention as sensors and luminescent anticounterfeiting. Herein, selective solvent molecule response and accordingly luminescence switching were discovered in 0D [EtPPh 3 ] 2 [SbCl 5 ] (1, EtPPh 3 = ethyltriphenylphosphonium). More than a dozen kinds of solvent molecules have been tested to find out the selection rule for molecule absorption in 1, which is demonstrated to be the size effect of guest molecules. Confirmed by crystal structural analysis, only the solvents with molecular volume less than 22.3 Å 3 could be accommodated in 1 leading to the solvatochromic photoluminescence (PL). The mechanism of solvatochromic PL was also deeply studied, which was found to be closely related to the supramolecular interactions between solvent molecules and the host material. Different functional groups of the solvent molecule can affect its strength of hydrogen bonding with [SbCl 5 ] 2− , which is crucial for the distortion level of [SbCl 5 ] 2− unit and thus results in not only distinct solvatochromic PL but also distinct thermochromic PL. In addition, they all show typical self-trapped exciton triplet emissions. The additional supramolecular interactions from guest molecules can enhance the photoluminescence quantum yield to be as high as 95%.