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 μV/K and a power factor of 10 μW/m ⋅ K², surpassing Ag₄TTBQ and the other reported silver-based c-CPs. Furthermore, terahertz spectroscopy demonstrates high charge mobilities exceeding 130 cm²/V ⋅ s in both Ag₄TTHQ and Ag₄TTBQ.