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), H₄<b>L</b>-OEt and H₄<b>L</b>-OH. Four CMOFs, <b>Zn-L</b>-OEt, <b>Zn-L</b>-OH, <b>Cd-L</b>-OEt, and <b>Cd-L</b>-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 <b>L</b>-OEt and <b>L</b>-OH ligands to form noninterpenetrated 4, 8-c <b>4,8T41</b> zinc CMOFs (<b>Zn-L</b>-OEt and <b>Zn-L</b>-OH) and 2-fold interpenetrated 4-c diamondoid (<b>dia</b>) cadmium CMOFs (<b>Cd-L</b>-OEt and <b>Cd-L</b>-OH), respectively. At a ligand concentration of 24 μM, H₄<b>L</b>-OEt and H₄<b>L</b>-OH showed negligible luminescent quenching by <i>RR</i>- and <i>SS</i>-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 <i>RR</i>-HB over <i>SS-</i>HB, with <b>Zn-L</b>-OEt exhibiting the highest quenching ratio (<i>K</i>_sv(<i>RR</i>)/<i>K</i>_sv(<i>SS</i>)) of 1.624. This work highlights the potential of CMOFs in enantioselective sensing applications.