A stable tetraphenylethene derivative: aggregation-induced emission, different crystalline polymorphs, and totally different mechanoluminescence properties

Two crystalline polymorphs of TMPE, with the space groups P2(1)(c) and C2, are cultured from different solvent mixtures and display apparent blue fluorescence with the characteristic of aggregation induced emission (AIE). Excitedly, the P2(1)(c) crystal exhibits easily observed mechanoluminescence (ML), while there is no mechanoluminescence for the C2 crystal. Careful investigation of their crystal structures and three analogues demonstrates that the special molecule packing of TMPE in the P2(1)(c) crystal accounts for its exciting efficientML performance, providing some information to understand the structure-property relationship of efficient organic ML materials.