Polymorphism-Dependent and Mechanochromic Luminescent Molecules

Organic mechanochromic luminescent materials are under extensive research because of their potential applications in sensors and security. An ideal mechanochromic material should comprise high fluorescent quantum yield in the solid state, significant fluorescent change after mechanical stimulus and high sensitivity to mechanical force, however, few materials reported till now meet all the requisites due to that our limited understanding of mechanochromic mechanism restrains the exploration of high-contrast mechanochromic materials. In order to investigate the mechanochromic mechanism, correlation of mechanochromic luminescence and polymorphic emission is one popular and effective method. During the recent years, great attentions have been paid to cultivate polymorphic crystals with different emissions for mechanochromic molecules. In this review, we s we summarize the polymorphism-dependent and mechanochromic luminescent molecules reported so far, as well as discuss their structure-property relationships, which may provide basic insights for design and synthesis of high-contrast mechanochromic materials. The mechanochromic compounds discussed in this review are categorized into different classes based on their chromophores, including tetraphenylethylene, phenylethylene, BODIPY, polycyclic aromatic hydrocarbon and etc.