Helical Chain Engineering in Chiral Metal-Organic Frameworks for Significantly Enhanced Circularly Polarized...

The efficient amplification of molecular chirality into macroscopic chiroptical responses remains a key challenge in the development of circularly polarized photoluminescence (CPL) materials. Herein, we demonstrate that constructing well-defined helical chains within chiral metal-organic frameworks (CMOFs) serves as a powerful strategy to address this challenge. A pair of enantiomorphic CMOFs, D/L-Zn-2, featuring pronounced helical chains, and their nonhelical layered counterpart, D/L-Zn-1, were designed and synthesized from identical chiral ligands for a direct comparative study. Strikingly, the helical framework D/L-Zn-2 exhibits an order-of-magnitude enhancement in the luminescence dissymmetry factor (|g_lum| = 3.67 × 10^-2), compared to that of D/L-Zn-1. This dramatic enhancement is attributed to the helical superstructure, which acts as a chiral amplification matrix by providing a highly dissymmetric microenvironment for the emissive chromophores and promoting a more-delocalized excited state. This work not only presents high-performance CPL-active materials but also establishes helical engineering as a fundamental and effective design principle for advanced chiroptical systems.