Multi-stimuli responsive cyanostilbene derivatives: pH, amine vapor sensing and mechanoluminescence

Two multi-stimuli responsive compounds 1 and 2, obtained by the introduction of carboxyl group to cyanostilbene skeleton, showed fluorescence response to pH change, amine vapors and mechanical stimulus. After scrutinizing their single crystal structures and comparing them with those of reference compounds 3 and 4, the molecules were found to take face-to-face stacking through multiple π-π interactions in restraining the non-radiative relaxation of excited state, which led to mechanoluminescence (ML) during fracturing process of crystal. The discovery of these novel ML luminogens provides guidelines for the design of pure organic ML materials.