Elucidating the Excited State of Mechanoluminescence in Organic Luminogens with Room‐Temperature Phosphorescence

Two stable, purely organic luminogens exhibit both mechano‐ (ML) and photoluminescence (PL) with dual fluorescence–phosphorescence emissions at room temperature. Careful analysis of the crystal structures, coupled with theoretical calculations, demonstrate that room‐temperature phosphorescence and ML properties are strongly related to molecular packing. In particular, the formation and fracture of molecular dimers with intermolecular charge‐transfer properties has a significant effect on intersystem crossing, as well as excited triplet state emissions, in both PL and ML processes. Light & Crunchy: Two stable purely organic luminogens, CzS‐CH3 and CzS‐C2H5, exhibit mechano‐ (ML) and photoluminescence (PL) with dual fluorescence–phosphorescence (F–P) emissions at room temperature. A well‐understood PL process functions as a template, allowing visualization of an unknown ML excited state.