Bright LanthanideIII 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.