Bright Lanthanide^III Triboluminescence despite Low Photoluminescence, and Dual Triboluminescence and Mechano‐Responsive Photoluminescence

Abstract In pursuit of a new family of mechanically responsive luminescent materials, it is aimed to differentiate triboluminescence (TL) from photoluminescence (PL). A β‐diketonate ligand with tert‐butyl groups (2,2,6,6‐tetramethylheptane‐3,5‐dionate: tmh) is selected to quench Eu^III‐centered PL via ligand‐to‐metal charge transfer, whereas tmh provides efficient photosensitization of Tb^III ions. Bright TL is observed from the Eu^III and Tb^III homodinuclear complexes despite the fact that their PL quantum yields differed by a factor of >50. Nanomechanical tests reveal the ductility of the crystals, suggesting they are ideal for accumulating deformation energy before breakage. Furthermore, a TL/PL color difference is observed for a Tb^III/Eu^III heterodinuclear complex, and grinding results in mechanochromic luminescence (MCL); this is the first example of a dual TL‐ and MCL‐active lanthanide^III coordination compound. The photophysical properties before, during, and after grinding are investigated and correlated with powder and single‐crystal crystallographic data.