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.
Original language | English |
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Pages (from-to) | 32183-32193 |
Number of pages | 11 |
Journal | Physical Chemistry Chemical Physics |
Volume | 17 |
Issue number | 48 |
DOIs | |
State | Published - 2015 |