Issue 48, 2015

Photoinduced water splitting via benzoquinone and semiquinone sensitisation


The splitting of water into H˙ and OH˙ radicals by sensitisation of a redox-active chromophore with sunlight may eventually become a viable way of producing unlimited, clean and sustainable energy. In this work, we explore the possibility of photo-oxidation of water via sensitisation of benzoquinone with ultraviolet (UV) light in the hydrogen-bonded complex of benzoquinone with a single water molecule. Using state-of-the-art quantum chemical calculations, the mechanisms of electron/proton transfer reactions between photoexcited benzoquinone and water are characterised. In the benzoquinone–H2O complex, photoexcitation of the chromophore leads to the population of locally excited ππ* and nπ* singlet states, which are coupled to hitherto unknown charge-transfer states. In the latter, an electron is transferred from the oxygen atom of the water molecule to the lowest π* orbital of benzoquinone. These charge-separated states drive the transfer of a proton from the water molecule to the carbonyl acceptor site, yielding the semiquinone–OH˙ biradical. Upon absorption of a second UV photon, the semiquinone radical may undergo O–H bond fission, which generates an H˙ radical and restores the benzoquinone photocatalyst. Our computational results shed light on long-standing questions regarding the nature of the photoreactive electronic states in the aqueous photochemistry of benzoquinone.

Graphical abstract: Photoinduced water splitting via benzoquinone and semiquinone sensitisation

Article information

Article type
02 Jul 2015
29 Sep 2015
First published
06 Oct 2015
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2015,17, 32183-32193

Photoinduced water splitting via benzoquinone and semiquinone sensitisation

T. N. V. Karsili, D. Tuna, J. Ehrmaier and W. Domcke, Phys. Chem. Chem. Phys., 2015, 17, 32183 DOI: 10.1039/C5CP03831F

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