A Non-enantiopure H8-BINOL Metal-Organic Framework for Enantioselective Fluorescence Sensing

A major challenge in chiral sensing technologies is the reliance on enantiopure materials to differentiate between enantiomers, as their interactions with a chiral system produce distinct detection signals. However, synthesizing and isolating enantiopure materials is often costly and time-consuming due to the difficulty of separating enantiomers. Here, we demonstrate that racemic materials can also function effectively as chiral sensors when the system exhibits non-inversion enantioselectivity. Fluorescent Cd(II) metal-organic frameworks (MOFs) were synthesised using enantiopure and racemic H8-BINOL-based ligands and their ability to enantioselectively sense aspartic acid dimethyl ester (Asp-diME) evaluated. Remarkably, the MOF synthesized from the racemic ligand retained measurable enantioselectivity, comparable to its enantiopure counterparts, highlighting its potential as a cost-effective and accessible alternative for chiral sensing. We further investigated the crystallization mechanism and found that secondary nucleation templated by the initial crystal plays a significant role in chiral induction during MOF formation, posing a challenge in obtaining a truly racemic MOF. These findings provide a promising strategy for designing chiral sensors based on racemic materials and underscore the importance of chiral induction in chiral MOF synthesis.