Multi-Stimuli-Responsive Mechanoluminescent Manganese Halide Toward External-Light-Free Photochemistry

Solvent-free mechanochemical photosynthesis offers significant advantages in enhancing reaction efficiency and minimizing environmental impact. However, the inherent opacity of conventional reactors greatly impedes their integration with photochemical pathways within the "dark box." In this regard, we synthesized a mechanoluminescent (ML) manganese halide (ETP)₂MnBr₄ (ETP = ethyltriphenylphosphonium) to trigger the sulfonylation reaction, achieving a series of alkenyl and allyl sulfones with 65%-85% yields, all without solvents and external light sources. Piezoresponse force microscope measurements and pressure-dependent dipole moment analysis indicate that mechanical stress enhances local piezoelectric response and thus leads to the intriguing mechanoluminescence. Furthermore, this ML (ETP)₂MnBr₄ exhibits multi-stimuli-responses with considerable piezochromism of redshift by 174 nm and an abnormal anti-thermal emission quenching. The increased crystal field strength associated with the decreased Mn-Br bond length leads to the stark piezochromism from green to red under high pressure. This study provides a promising ML manganese halide that enables potential applications in sustainable photochemistry, sensing and anti-counterfeiting.