Homochiral BINOL-Based Metal-Organic Frameworks for Luminescence Sensing of Hydrobenzoin Enantiomers

Luminescent chiral metal-organic frameworks (CMOFs) are promising candidates for the enantioselective sensing of important chiral molecules. Herein, we report the synthesis and characterization of Zn and Cd CMOFs based on 1,1′-bi-2-naphthol (BINOL)-derived 3,3′,6,6′-tetra(benzoic acids), H₄L-OEt and H₄L-OH. Four CMOFs, Zn-L-OEt, Zn-L-OH, Cd-L-OEt, and Cd-L-OH, based on these ligands were crystallographically characterized. Zinc cations form 8-connected (8-c) penta-metallic secondary building units (SBUs), while cadmium cations form 4-c trimetallic SBUs. These SBUs are linked by 4-c L-OEt and L-OH ligands to form noninterpenetrated 4, 8-c 4,8T41 zinc CMOFs (Zn-L-OEt and Zn-L-OH) and 2-fold interpenetrated 4-c diamondoid (dia) cadmium CMOFs (Cd-L-OEt and Cd-L-OH), respectively. At a ligand concentration of 24 μM, H₄L-OEt and H₄L-OH showed negligible luminescent quenching by RR- and SS-hydrobenzoin (HB) enantiomers with Stern-Völmer constants of 29-89 M^-1. In contrast, CMOFs displayed efficient quenching by HB enantiomers with Stern-Völmer constants of 583-1200 M^-1, due to significant HB preconcentration in CMOF channels via favorable host-guest interactions between CMOF frameworks and HB molecules. The CMOFs demonstrated luminescence quenching selectivity for RR-HB over SS-HB, with Zn-L-OEt exhibiting the highest quenching ratio (K_sv(RR)/K_sv(SS)) of 1.624. This work highlights the potential of CMOFs in enantioselective sensing applications.