Space Group Modulated Upconversion and Mechanoluminescence in [YbEu] Cocrystal Complexes

Lanthanide complexes exhibiting stimuli‐responsive luminescence, such as upconversion (UC) and mechanoluminescence (ML), are promising for optoelectronics and sensing applications. However, the simultaneous integration of these two properties within a single material remains a challenge, as their emission mechanisms often have different structural requirements. Herein, we report a space group regulation strategy to optimize both UC and ML in cocrystal assemblies. A known mononuclear [Eu] complex crystallizes in the orthorhombic P 2 1 2 1 2 1 space group. Influenced by lanthanide contraction, chirality, and doping ratio, homochiral and racemic [YbEu] heterometallic cocrystal systems are constructed, which crystallize in the P 2 1 and P 2 1 /c space groups, respectively. The highly symmetric P 2 1 2 1 2 1 structure exhibits strong ML but no UC; the centrosymmetric P 2 1 /c lattice affords efficient UC yet quenches ML; most remarkably, the noncentrosymmetric polar P 2 1 architecture uniquely supports both remarkable properties. Cooperative sensitization UC upon 980 nm excitation and an 8.4‐fold enhancement in Eu 3+ ‐centered ML compared to the racemic analog, are attributed to an optimal energy transfer pathway and a piezoelectric‐active structure. Furthermore, the ML intensity shows a linear force‐responsiveness (10–50 N) with high sensitivity, highlighting its sensing potential. This work establishes a strategy for designing multifunctional lanthanide‐organic materials.