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Issue 48, 2015
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Photoinduced water splitting via benzoquinone and semiquinone sensitisation

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Abstract

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

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Publication details

The article was received on 02 Jul 2015, accepted on 29 Sep 2015 and first published on 06 Oct 2015


Article type: Paper
DOI: 10.1039/C5CP03831F
Phys. Chem. Chem. Phys., 2015,17, 32183-32193
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    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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