Recent Advances in Mechanism of AIE Mechanochromic Materials

Organic mechanochromic materials(also known as piezochromic materials), whose color or emission changes under mechanical force, have attracted great interest owing to their potential applications in pressure sensors, rewritable materials, optical storage, and security ink. Organic mechanochromic materials with aggregation-induced emission(AIE) features have better development prospects and research value owing to their excellent optical properties. To date, mechanochromism has mostly been realized by means of mechanical grinding. Nevertheless, the magnitude of the grinding force is usually uncontrollable and its direction is anisotropic, making it awkward to study the mechanism of mechanochromic materials. On the contrary, hydrostatic pressure, whose magnitude and direction are controllable, is a more valid and governable method to investigate the mechanism of mechanochromic materials, which can help us to construct a meaningful structure-property relationship and understand the latent origin of the mechanochromism. Furthermore, it is conducive to developing other mechanochromic material systems with desired chemical and physical properties. In this review, we focus on the recent progress in the mechanism of organic mechanochromic materials with AIE features under hydrostatic pressure. Four types of mechanisms are included: intermolecular interaction change, intramolecular conformation change, transformation from locally excited state to intramolecular charge-transfer state, and intra- and inter-molecular effects induced by hydrostatic pressure, respectively.