pH‐Switchable Excited‐State Dynamics of Iridium(III) Photosensitizers Bearing an N‐Heterocyclic Imine‐Functionalized 2,2’‐Bipyridine
(2025) Chemistry: A European Journal — Vol. 0:e03127, n° 0:e03127, p. 0:e03127 (2025)
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- Authors
Troian‐Gautier, Ludovic 
Dielmann, Fabian
- Abstract
- We report the design, synthesis, and comprehensive photophysical characterization of a new class of heteroleptic IrIII complexes featuring a strongly electron-donating 4,4′-bis(N-heterocyclic imine)-2,2′-bipyridine (bpy-NHI) ligand. The bpy-NHI ligand was synthesized on a multigram scale via a seven-step sequence and fully characterized. Reaction with the dimer [Ir(ppy)2Cl]2 afforded the target complex [Ir(ppy)2(bpy-NHI)]+, whose electronic structure was probed by (spectro)electrochemistry as well as by steady-state and time-resolved spectroscopy. Compared to the parent [Ir(ppy)2(bpy)]+ complex, the new complex exhibits a significantly altered redox profile, including a novel irreversible oxidation at 0.4 V vs Fc+/Fc and the absence of the typical bpy-centered reduction, consistent with the strongly electron-donating nature of the NHI substituents. The high basicity of the NHI substituents enabled modulation of the excited-state properties via protonation, leading to unusual excited-state dynamics where the metal-to-ligand charge-transfer state switches between bpy- and ppy-based character. In the protonated form, the complex is able to bind chloride ions, which was qualitatively detected by changes in the ground-state absorption of the complex. These findings establish bpy-NHI as a powerful and sensitive electron-rich ligand platform for modulating the photophysical and electrochemical properties of Ir(III) complexes, opening new opportunities for the design of photosensitizers with tailored excited-state properties.
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Citations
Lempereur, S., Glaser, F., Franzen, J. H., Schöndorf, L., Siedl, M., Troian‐Gautier, L., & Dielmann, F. (2025). pH‐Switchable Excited‐State Dynamics of Iridium(III) Photosensitizers Bearing an N‐Heterocyclic Imine‐Functionalized 2,2’‐Bipyridine. Chemistry: A European Journal, 0:e03127(0:e03127), 0:e03127. https://doi.org/10.1002/chem.202503127 (Original work published 2025)