Halide-driven quenching of iron NHC complex: unlocking new pathways in photochemical dynamics Katerina Achilleos, Ludovic Troian Gautier UCLouvain, Belgium Iron-based N-heterocyclic carbene (NHC) complexes have emerged as versatile and efficient photosensitizers, due to their favorable redox properties and tunable electronic structure offering important advantages in light- driven reactions, such as energy transfer and electron transfer mechanisms. [1] Recently, some studies have revealed that halides (Cl – , Br – , I – ) can effectively quench the excited states of these complexes, providing that sufficient concentrations of halides are used. Indeed, one of the biggest challenges in using the Iron-based NHC photosensitizers for bimolecular excited-state electron transfer is their extremely short excited-state lifetimes. [2] The interaction between halides and Iron NHC complexes not only influences the efficiency of energy and electron transfer processes but also initiates new pathways for controlling photochemical reactions. [2] In here, we report an innovative approach that leverages electrostatic interactions to pre-associate iron photosensitizers and halides, thus eliminating the need for diffusion. To do so, we synthesized a novel Iron based-NHC complex functionalized with N-methyl-pyridinium groups, thereby leading to an overall tri-cationic photosensitizer. The novel photosensitizers were fully characterized, including molar absorption coefficient (ε) as well as steady-state and time-resolved luminescence across a wide range of solvents. Excited-state quenching experiments with halides were conducted to determine the quenching rate constants (k q ) through steady-state and time-resolved luminescence measurements, further revealing the impact of halide-induced quenching on the behavior of these complexes. Finally, proof of excited-state electron transfer was obtained using transient absorption spectroscopy, with time resolution that ranged from femtoseconds to microseconds ; Overall, the ability to control and modulate excited-state behavior through halide quenching could have meaningful applications in areas such as catalysis, energy conversion, and the development of bio-photochemical applications. [3] References 1. Hill, C. L., et al. "The Role of Iron NHC Complexes in Photochemical Catalysis and Energy Conversion." Chemical Reviews , 2014, 114(18), 9015-9047. DOI: 10.1021/cr500213f 2. De Kreijger, S., et al.“Investigation of the Excited-State Electron Transfer and Cage Escape Yields Between Halides and a Fe (III) Photosensitizer.” Journal of the American Chemical Society , 2024, 146(15), 10286–10292. DOI: 10.1021/ jacs.4c02808. 3. Leigh, D. A., et al. "NHC-Functionalized Iron Complexes in Photochemical and Catalytic Applications. " Nature Reviews Chemistry, 2020, 4, 129-144. DOI: 10.1038/s41570-019-0107-7
P02
© The Author(s), 2025
Made with FlippingBook Learn more on our blog