PerspectiveInorganic Chemistry

Iron hits the mark

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Science  18 Jan 2019:
Vol. 363, Issue 6424, pp. 225-226
DOI: 10.1126/science.aav9866

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Solar energy can enable our society to thrive as we endeavor to reduce our dependence on fossil fuels. However, the Sun is an intermittent form of energy. Solar-cell technology is well suited for daytime electricity generation and usage, but our society uses energy around the clock. Thus, it is not only important to generate electricity for daytime use but also to store solar energy for nighttime use. Chemists see huge potential in molecules and materials that absorb light (that is, solar energy) and use that energy to generate electrons that then carry out chemical reactions to turn low-energy feedstocks into high-energy fuels. To date, the transition metal complex (TMC) photosensitzers that have sufficiently long excited-state lifetimes to enable this chemistry (1) contain expensive and scarce metals, such as complexes of ruthenium (Ru), osmium, and iridium. On page 249 of this issue, Kjær et al. (2) report an iron (Fe)–based photosensitizer with a quantum efficiency surpassing that of [Ru(bpy)3]2+ (where bpy is 2,2′-bipyridine), the historical standard bearer. Furthermore, the new iron-based photosensitizer has an excited-state lifetime of 2 ns, which is sufficiently long to transfer electrons to other compounds (see the figure).