Molecular recognition could have applications in fields like sensing, information storage, or anti-counterfeiting. The recognition between two solid-state crystalline materials, however, had not been reported thus far.

Zeping Wang, Xiaoying Huang, Fujian Institute of Research on the Structure of Matter, The Chinese Academy of Sciences, Fuzhou, Kezhao Du, Fujian Normal University, Fuzhou, China, and colleagues have synthesized two isomers of an antimony-based ionic liquid hybrid metal halide (ILMH), namely, α-[Bmmim]₂SbCl₅ (1, Bmmim = 1-butyl-2,3-dimethylimidazolium) and β-[Bmmim]₂SbCl₅ (2). Crystals of chiral 2 can transform into crystals of achiral 1 when they are in contact under ambient conditions (pictured), demonstrating an unusual phenomenon called crystalline phase recognition (CPR).

The distinct photoluminescent colors of 1 and 2 allowed the team to observe the CPR in situ. The transition first occurs at the initial contact area and then spreads spontaneously throughout the entire crystal. The process is called a domino phase transition. The results could have implications, e.g., for the field of time-resolved information encryption.

• Crystalline Phase Recognition induced Domino Phase Transition and Luminescent Switching for Advanced Information Encryption,
  Zhizhuan Zhang, Yangpeng Lin, Jiance Jin, Liaokuo Gong, Yingchen Peng, Ying Song, Nannan Shen, Zeping Wang, Kezhao Du, Xiao-Ying Huang,
  Angew. Chem. Int. Ed. 2021.
  https://doi.org/10.1002/anie.202110088