Enhancing Chiral Site Density in Covalent Organic Frameworks Enables Efficient SERS-Based Enantioselective Discrimination

Surface-enhanced Raman scattering (SERS) enables simultaneous molecular identification and chiral discrimination, yet its broader application is often restricted by the limited availability of robust, reproducible, and universally applicable chiral sensing platforms. Herein, we demonstrate that covalent organic frameworks (COFs) offer a versatile platform for constructing stable and highly enantioselective SERS substrates. A three-dimensional chiral COF (SU-1) was synthesized via a "two-in-one" strategy using a single enantiopure binaphthol-derived monomer bearing both aldehyde and amine functionalities. This self-condensation approach eliminates achiral components and achieves the highest reported density of chiral binaphthyl units (2.05 mmol/g) among the known COFs. For comparison, a structurally analogous COF (SU-2) with lower chiral site density was synthesized via conventional co-condensation of a chiral binaphthol-based tetrabenzaldehyde and p-phenylenediamine. Upon incorporation of gold nanoparticles, both frameworks were evaluated as SERS-active platforms for the enantioselective sensing of a variety of small aromatic molecules. SU-1 exhibited significantly enhanced enantioselectivity and signal reproducibility relative to SU-2, highlighting the effectiveness of the "two-in-one" strategy in amplifying chiral recognition. This work presents a generalizable approach for constructing high-performance chiral COF-based SERS substrates and advances the application of crystalline porous materials in enantiomeric analysis.