Geometry-Identical Welding Unlocks Isoelectronic Engineering of Conductive Covalent Organic Frameworks

The development of effective and succinct molecular engineering strategies for electrically conductive and structurally robust materials underpins a wide scope of electronic applications from the bottom. In this work, we construct a new family of conductive covalent organic frameworks (COFs) composed of nickel phthalocyanine (NiPc) units fused by a single piperazine and dioxin linkage via aromatic nucleophilic substitution of octafluoro-substituted NiPc with the other two size- and symmetry-identical NiPc monomers peripherally equipped with amino and hydroxyl groups, respectively. This geometrically identical wielding of NiPc fragments not only affords high crystallinity by minimizing the crosslinking errors of the monomers but also yields a pair of isoelectronic COFs with only a structural difference on a single site from their piperazine and dioxin linkages. This subtle difference results in a pronounced modulation of the electrical properties of two COFs, as evidenced by their distinct bulk conductivities, which span two orders of magnitude (6 × 10^{- 4} S cm^{- 1} vs. 7 × 10^{- 6} S cm^{- 1}). Further iodine incorporation enables substantial conductivity enhancements of 300% and 500% in the piperazine- and dioxin-linked COFs (NiPc-NH and NiPc-O). When integrated into chemiresistive devices, the two isoelectronic COFs show discriminated electronic responses to NO and NO₂, allowing straightforward identification and quantification of these species, which would otherwise be challenging to distinguish with a single material.