Very bright mechanoluminescence and remarkable mechanochromism using a tetraphenylethene derivative with aggregation-induced emissionElectronic supplementary information (ESI) available: Details of the synthesis; structural information for the compound (NMR, IR, and mass spectra); Tables S1-S5; Fig. S1-S11. CCDC 1037840 and 1057432. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5sc00466g

Organic materials exhibiting mechanoluminescence (ML) are promising for usage in displays, lighting and sensing. However, the mechanism for ML generation remains unclear, and the light-emitting performance of organic ML materials in the solid state has been severely limited by an aggregation-caused quenching (ACQ) effect. Herein, we present two strongly photoluminescent polymorphs ( i.e. , C g and C b ) with distinctly different ML activities based on a tetraphenylethene derivative P 4 TA. As an aggregation-induced emission (AIE) emitter, P 4 TA perfectly surmounted the ACQ, making the resultant block-like crystals in the C g phase exhibit brilliant green ML under daylight at room temperature. The ML-inactive prism-like crystals C b can also have their ML turned on by transitioning toward C g with the aid of dichloromethane vapor. Moreover, the C g polymorph shows ML and mechanochromism simultaneously and respectively without and with UV irradiation under a force stimulus, thus suggesting a feasible design direction for the development of efficient and multifunctional ML materials. Two photoluminescent polymorphs exhibit different mechanoluminescence activities and mechanochromic behaviors.