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

ABSTRACT 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.