Control of the Hydroquinone/Benzoquinone Redox State in High-Mobility Semiconducting Conjugated Coordination Polymers

Conjugated coordination polymers (c-CPs) are unique organic-inorganic hybrid semiconductors with intrinsically high electrical conductivity and excellent charge carrier mobility. However, it remains a challenge in tailoring electronic structures, due to the lack of clear guidelines. Here, we develop a strategy wherein controlling the redox state of hydroquinone/benzoquinone (HQ/BQ) ligands allows for the modulation of the electronic structure of c-CPs while maintaining the structural topology. The redox-state control is achieved by reacting the ligand TTHQ (TTHQ=1,2,4,5-tetrathiolhydroquinone) with silver acetate and silver nitrate, yielding Ag4TTHQ and Ag4TTBQ (TTBQ=1,2,4,5-tetrathiolbenzoquinone), respectively. In spite of sharing the same topology consisting of a two-dimensional Ag-S network and HQ/BQ layer, they exhibit different band gaps (1.5 eV for Ag4TTHQ and 0.5 eV for Ag4TTBQ) and conductivities (0.4 S/cm for Ag4TTHQ and 10 S/cm for Ag4TTBQ). DFT calculations reveal that these differences arise from the ligand oxidation state inhibiting energy band formation near the Fermi level in Ag4TTHQ. Consequently, Ag4TTHQ displays a high Seebeck coefficient of 330 mu V/K and a power factor of 10 mu W/m & sdot; K2, surpassing Ag4TTBQ and the other reported silver-based c-CPs. Furthermore, terahertz spectroscopy demonstrates high charge mobilities exceeding 130 cm2/V & sdot; s in both Ag4TTHQ and Ag4TTBQ. This study introduces a novel synthetic strategy to modulate the electronic band structure of conjugated coordination polymers (c-CPs) through control of the redox state of hydroquinone/benzoquinone ligands during synthesis. We successfully synthesized two distinct semiconducting c-CPs, Ag4TTBQ(TTBQ=1,2,4,5-tetrathiolbenzoquinone) and Ag4TTHQ(TTHQ=1,2,4,5-tetrathiolhydroquinone), by reacting TTHQ with silver nitrate and silver acetate, respectively. Despite sharing the same topological structure, charge transport measurements and DFT calculations reveal significant differences in their electronic structures. Notably, Ag4TTHQ demonstrates superior thermoelectric performance compared to other silver-based c-CPs. This research unveils a pioneering approach to finely tune the electronic band structure and properties of c-CPs, and paves the way for advanced applications in high-performance thermoelectric and electronic devices.+ image