Enhancement and acid‒base response of redox conduction in a pyridine-functionalized 2D bis(terpyridine)cobalt(II) coordination polymer

Abstract Coordination polymer thin films based on bis(terpyridine)metal(II) motifs are promising electrofunctional materials owing to their intrinsic redox activity and structural tunability. However, ligand-functionalization strategies for modulating their electronic properties remain fundamentally underdeveloped, particularly for controlling charge transport and external stimuli responsiveness. Here, we report a pyridine-cored tris(terpyridine) ligand ( 2 ) and its incorporation into a two-dimensional bis(terpyridine)cobalt(II) polymer thin film ( 2-Co ) via a liquid‒liquid interfacial coordination reaction. Structural analyses confirmed the formation of a uniform nanosheet with exchangeable counter anions. Anion-exchange with hydrogen sulfate induces partial protonation of the pyridine core, enabling chemical modulation of the electronic structure. Electrochemical measurements revealed that 2-Co exhibits redox activity based on the [Co(tpy) 2 ] 2+ /[Co(tpy) 2 ] + couple in both protonated and deprotonated states. Notably, potential-dependent conductivity measurements revealed that 2-Co reaches a maximum conductivity of 1.2 mS cm −1 , which is three orders of magnitude higher than that of the benzene-cored analog. Furthermore, protonation of the pyridine core suppressed the conductivity to one-third, demonstrating the ability to control redox conduction in a proton-responsive manner. This work establishes a general design principle for coupling electronic and chemical (acid–base) control in redox-conducting coordination polymers.