Stable Radical Iridium(III) Complexes with Tunable Panchromatic Absorption

Inorganic Chemistry. 2025. Vol. 64. No. 50. P. 24579–24593.

Tatarin S., Zhuravlev I., Minin M., Emets V., Arsenyeva K., Piskunov A., Stanislav I. Bezzubov

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 o-semiquinone/o-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 o-aminophenolate form due to intramolecular H-bonding, while the o-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.

Keywords: spectroscopy, спектроскопия, Iridium, Redox-active ligands, Иридий, редокс-активные лиганды