Stable Radical Iridium(III) Complexes with Tunable Panchromatic Absorption

To date, the design of stable panchromatic metal complexes simultaneously exhibiting reversible redox behavior remains a challenging endeavor, underscoring the need for new ligand platforms to expand their absorption spectrum. In this study, we report the synthesis and characterization of octahedral bis-cyclometalated iridium(III) complexes with redox-active <i>o</i>-semiquinone/<i>o</i>-iminosemiquinone ancillary ligands, which exhibit exceptional chemical stability and intense absorption up to the infrared (∼1050 nm) region. The complexes demonstrate independently tunable absorption maxima in the UV-vis and vis-NIR regions by modification of the cyclometalated scaffold and ancillary ligand, respectively, alongside predominantly reversible electrochemical behavior. The introduction of the carboxylate fragment into the ancillary ligand enables the electron-transfer process to the semiconductor, which was further validated in TiO₂ photoanodes for dye-sensitized solar cells. The complexes also displayed pronounced photothermal conversion under IR irradiation, highlighting their potential in photothermal therapy. Tailoring the ancillary ligand allows for stabilization of its coordinated <i>o</i>-aminophenolate form due to intramolecular H-bonding, while the <i>o</i>-iminoquinone form can be accessed through oxidation by a silver(I) salt, thereby expanding the diversity of accessible iridium species. This study offers a simple and efficient strategy toward stable, panchromatic metalloradicals with high tunability and functionality to advance their applicability in various energy-demanding transformations.