Increasing Cage Escape Yields for Halide Oxidation in Aqueous Solutions Using Ir(III) Photosensitizers with π-Extended Aromatic Ligands
(2026) Inorganic Chemistry — Vol. 65, n° 24, p. 13311-13326 (2026)
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Olivier, Yoann 
- Abstract
- A series of five Ir(III) photosensitizers featuring π-extended aromatic ligands is reported for iodide, bromide, and chloride photo-oxidation in acetonitrile/water (50:50) mixtures. All photosensitizers exhibited excited-state reactivity toward iodide, bromide, and chloride, with quenching rate constants in the (1.2− 2.1) 10 10 M −1 s −1 , (0.8−4.8) 10 9 M −1 s −1 , and (0.049−1.3) 10 8 M −1 s −1 range, respectively. Nanosecond transient absorption spectroscopy confirmed electron transfer from the halides to the excited photosensitizers, with cage escape yields (Φ CE) that were significantly higher in acetonitrile than in acetonitrile/water mixtures. In acetonitrile, up to unitary cage escape yields were obtained for iodide, bromide, and chloride oxidation. In water-enriched conditions, those yields decreased drastically, but the introduction of π-extended aromatic ligands allowed to maintain appreciable cage escape yields (Φ CE = 0.02−0.32). ■ INTRODUCTION The global energy crisis, driven by the rapid depletion of fossil fuels and the escalating demand for energy, has become one of the most pressing challenges of the 21st century. Fossil fuels, which currently account for the majority of the world's energy supply, are not only finite but also contribute significantly to environmental pollution and climate change. As a result, there is an urgent need to develop renewable energy sources that can meet the growing energy demands while mitigating environmental impacts. Among the various renewable energy technologies, the storage of solar energy in chemical bonds of small molecules, so-called solar fuels, has emerged as a promising solution. 1−9 This approach offers a way to store and transport solar energy efficiently, addressing the intermittent nature of solar power. Among the various solar fuels, hydrogen gas (H 2) stands out as a highly promising candidate for large-scale energy storage and distribution. 10 Hydrohalic acid (HX) splitting involves the thermodynamically challenging process of converting HX to H 2 and the corresponding halogen (X 2). The reverse reaction releases free energy, making this approach particularly advantageous. Unlike water oxidation, which requires four electrons and multiple proton-coupled electron transfer steps, halide oxidation only involves a simpler two-electron transfer process and does not require protons. While both HX splitting and water splitting are significant for producing hydrogen, the kinetic barriers and the complexity of water oxidation pose substantial challenges. 11 This makes HX splitting (where X = Cl − , Br − , or I −) a highly desirable reaction for solar fuel production. 12
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Citations
De Kreijger, S., Cristofaro, S., Olivier, Y., Elias, B., & Troian-Gautier, L. (2026). Increasing Cage Escape Yields for Halide Oxidation in Aqueous Solutions Using Ir(III) Photosensitizers with π-Extended Aromatic Ligands. Inorganic Chemistry, 65(24), 13311-13326. https://doi.org/10.1021/acs.inorgchem.5c05414 (Original work published 2026)