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

Abstract

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 P₄TA. As an aggregation-induced emission (AIE) emitter, P₄TA 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.