Fe( <scp>iii</scp> )-NHC photosensitizers matching Ru( <scp>ii</scp> ) performance in the oxidation of iodide to triiodide
(2026) Catalysis Science & Technology — Vol. 16, n° 16, p. 5269-5278 (2026)
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- Authors
Glaser, Felix 
Abudayyeh, Abdullah
- Abstract
- The development of sustainable photosensitizers capable of driving high-potential redox chemistry is a central challenge in the pursuit of solar-driven halide oxidation and solar-fuel generation. While noble-metal photosensitizers can promote halide oxidation, their scarcity and cost limit large-scale applicability. Iron-based N-heterocyclic carbene (NHC) complexes have emerged as promising alternatives, yet their short excited-state lifetimes still limit bimolecular photoreactivity. Here we report iodide oxidation to triiodide using the Fe(III) photosensitizer [Fe(L BMes) 2 ] + , which incorporates a Lewis-acidic dimesitylboron unit. This modification preserves the ∼2 ns LMCT excited-state lifetime and redox potentials of the parent [Fe(L) 2 ] + complex while enabling halide pre-association with association constant <5 M −1. Time-resolved and steady-state photoluminescence studies reveal efficient quenching of 2 LMCT states by I − , Br − , and Cl − in both acetonitrile and dichloromethane. Nanosecond transient absorption spectroscopy confirms excited-state electron transfer from iodide to [Fe(L BMes) 2 ] + *, yielding I 2˙− and the one-electron-reduced iron species with low cage-escape yields that are comparable to the parent [Fe(L) 2 ] +. Capitalizing on the Fe(III/II) reduction potential, the reduced photosensitizer is efficiently reoxidized by dissolved O 2 , preventing back-electron transfer and enabling accumulation of I 3 − under continuous irradiation. The results were benchmarked against an established Ru(II)-based photosensitizer with similar driving force for halide oxidation and O 2 reduction. All photosensitizers displayed similar efficiency in terms of triiodide formation and excellent photostability. These results identify these photosensitizers based on earth-abundant elements as sustainable alternatives to Ru-based systems.
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Citations
Achilleos, K., Glaser, F., Abudayyeh, A., & Troian-Gautier, L. (2026). Fe( <scp>iii</scp> )-NHC photosensitizers matching Ru( <scp>ii</scp> ) performance in the oxidation of iodide to triiodide. Catalysis Science & Technology, 16(16), 5269-5278. https://doi.org/10.1039/d6cy00340k (Original work published 2026)