The Influence of Molecular Packing on the Emissive Behavior of Pyrene Derivatives: Mechanoluminescence and Mechanochromism

Abstract Although some bright, organic mechanoluminescence (ML) luminogens with aggregation‐induced emission properties and twisted molecular structures are recently reported, those with planar structures and bright ML and their related effective design strategies are not yet explored, partially due to aggregation‐caused quenching in luminogens with planar structures. Herein, using the unique solid‐state packing style of pyrene, bright dual monomer‐excimer‐ML and excimer‐ML from two pyrene derivatives (Py‐Bpin and Py‐Br) with a simple, planar molecular structure are reported for the first time, and two analogs of pyrene and Py‐H are used for comparison. These four luminogens display similar optical properties in dilute solution but different luminescent properties in the solid state, mainly due to their different molecular packing. Interestingly, pyrene is mechanochromism (MC)‐ and ML‐inactive, while Py‐H is MC‐active, Py‐Bpin is MC‐ and ML‐active, and Py‐Br is ML‐active. The relationship between molecular packing and ML/MC properties is confirmed by analyzing single‐crystal structures and related experimental results, providing important information to further understand the mysterious ML process and opening a new way to design efficient luminogens with both MC and ML.