Molecular bridge engineering in covalent organic frameworks for enhanced electronic transport

Conductive two-dimensional covalent organic frameworks (2D COFs) possess intrinsic π-conjugation and long-range order, yet their electrical performance in thin-film devices remains constrained by grain boundaries and amorphous regions that interrupt charge transport. Here we report a simple and scalable strategy to overcome these limitations by bridging polycrystalline COF domains with molecularly dispersed conjugated polymers (CPs). Guided by electronic alignment, geometric compatibility, and chain-length criteria, we identify COF-CP combinations that exhibit markedly enhanced conductivity when assembled into heterostructures. By demonstrating that electrical property enhancement occurs only below the CP crystallization threshold, we show that bridging CPs require short-range ordered or near-amorphous configurations to effectively span COF grains and establish continuous transport pathways. This approach is compatible with wafer-scale fabrication and enables ppb-level NO₂ sensing by coupling COF porosity with CP-mediated charge transport. Our results establish a rational polymer-bridging strategy for COF-based electronic materials and identify key design parameters for its extension to other COF-CP systems.