Very bright mechanoluminescence and remarkable mechanochromism using a tetraphenylethene derivative with aggregation-induced emission

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.