Recognition-Based Chiral Amplification through Adaptive Locking

Chiral amplification in host-guest systems remains difficult to control because structures tend to be either too rigid to accommodate a guest or too flexible to maintain stable helicity. This is a limitation where binding of chiral substrates is a key to chiroptical induction and the production of, e.g., a circular dichroism (CD) or circularly polarized luminescence (CPL) response. Here, we introduce a supramolecular-based adaptive-locking chirality (ALC) strategy that integrates chirality induction and helicity control within a molecular organic cage (Cg). This cage is flexible and able to bind a broad range of chiral acids. After the capture of four guests and saturation of the four available binding sites, conformational locking of Cg occurs, which stabilizes a single helical configuration. Structural, spectroscopic, and kinetic analyses reveal a guest-dependent progression from rapid helix interconversion to a structure characterized by fully immobilized chirality. These structural changes were found to correlate directly with the emergence of increasingly strong chiroptical signals. The |g_abs| and |g_lum| values for the resulting complexes were found to reach 0.044 and 0.012. A quantitative correlation between desymmetrization as inferred from NMR spectroscopic analyses (Δν) and the |g_lum| values was observed. This enables a predictive assessment of the chiroptical performance for Cg and may provide a general strategy for evaluating a priori high-performance chiroptical materials.