Circularly polarized luminescence enhancement in rare-earth MOFs due to framework chirality and host–guest energy transfer

Chiral metal-organic frameworks (CMOFs) incorporating rare-earth ions hold great promise for circularly polarized luminescence (CPL) applications due to their structural tunability and strong emission. Herein, we report two pairs of enantiomeric rare-earth CMOFs synthesized via direct self-assembly of optically pure 1,3-bis((S)- or (R)-1-carboxyethyl)-1H-imidazol-3-ium chloride ([L/D-(H₂IDPA)⁺Cl⁻]) with lanthanide ions. The resulting Tb-based framework, L-Tb-1, exhibits intrinsic CPL with a dissymmetry factor (|g_lum|) of 0.016, attributed to efficient chirality transfer and the antenna effect. Upon introducing MnCl₄²⁻ as a luminescent guest into the framework channels, the CPL activity of L-Tb-2∙(MnCl₄²⁻) is markedly enhanced, achieving a |g_lum| of 0.071. Control experiments and spectral analysis confirm that this enhancement arises from synergistic host-guest energy transfer and chiral transfer. This work demonstrates a modular strategy for constructing CPL-active rare-earth CMOFs and provides a general design principle for tuning chiroptical properties via host-guest interactions.