Converting and storing sunlight into clean chemical fuels is an area full of promises, which represents one of the most important challenge of the current energy transition. The success of such an approach relies on the access to light-sensitive molecules combining several key properties including interesting excited-state redox properties and strong visible light absorption. In this field, iridium(III) complexes have recently emerged as potential candidates thanks to their exceptional photo- and redox stability as well as their highly tunable optoelectronic properties. However, their poor light harvesting in the visible region has largely precluded their use in solar energy conversion.
In our recent study published in the Journal of the American Chemical Society and performed in close collaboration with Dr. Ludovic Troian-Gautier (ULB) and the group of Prof. Gerald J. Meyer (UNC), we showed that Ir(III)-based compounds with strong visible light absorption may be obtained through rational ligand design. Strikingly, such an improvement was achieved without loss of photoreactivity. Our lead complex, Ir-bpph (in blue), was successful in performing light-driven charge separation and energy storage. Nanosecond transient absorption spectroscopy revealed that this molecule was able to oxidize a variety of organic substrates and halides upon light excitation. Finally, application of Marcus theory provided a small total reorganization energy of 0.7 eV implying small kinetic barriers for excited-state electron transfer. Hence, the Ir-bpph complex combines enhanced visible light absorption, strong photo-oxidizing ability, and low reorganization energy for fast electron transfer.
« Improved Visible Light Absorption of Potent Iridium(III) Photooxidants for Excited-State Electron Transfer Chemistry »
R. Bevernaegie, S. A. M. Wehlin, E. J. Piechota, M. Abraham, C. Philouze, G. J. Meyer, B. Elias*, and L. Troian-Gautier*, J. Am. Chem. Soc. 2020, 142, 2732−2737 (doi : 10.1021/jacs.9b12108)