A universal synthetic strategy for noncentrosymmetric lead oxyhalide frameworks with strong second-harmonic generation.

Hybrid lead halides possess a unique combination of structural flexibility, compositional tunability and bandgap adjustability, making them promising candidates for nonlinear optical (NLO) applications. However, realizing strong second-harmonic generation (SHG) responses remains a significant challenge due to their inherent ionic architecture, which favors ideal PbX6 octahedral geometry and hinders oriented alignment of asymmetric primitives. Herein, we present an inorganic-organic dual-site synergistic strategy that combines π-conjugated aromatic units and stereoactive inorganic building blocks to induce noncentrosymmetry and substantial macroscopic polarization. The well-aligned coordination between Pb2+ centers and meta-dicarboxylates facilitates the construction of a new family of fifteen noncentrosymmetric lead oxyhalide frameworks. These frameworks featuring NLO-active [PbX2O6] (X = Cl-, Br-, I-) units allow for bandgap modulation dependent on the halide species, and the ordered arrangement of 5-functionalized isophthalate linkers directs the primitive superposition. Among them, the Br-substituted isophthalate-based lead iodide exhibits record-level performance for hybrid lead halides: a phase-matching SHG response of 11.0 × KH2PO4 at 1064 nm, a birefringence of 0.179 at 546 nm, and a corresponding UV cutoff edge. Moreover, this synthetic strategy establishes direct coordination linkage between organic phosphorescent centers and inorganic light-harvesting lead halide motifs, enabling tunable long-lived afterglow emission up to 7.36 ms.