highlight 7 2017

We are currently investigating bimolecular electron transfer reactions in room temperature ionic liquids (RTILs). The reaction is triggered by the optical excitation of a dye (D) which leads to an increase of its reductive power and enables electron transfer to an electron acceptor (EA). Transient absorption (TA) measurements, depicted in 1, revealed a peculiar behaviour in this unusual solvent: After about 10 ns, the D+ signal as well as the ground state bleach are rising even though the excited state has already decayed.

A systematic spectroscopic investigation showed the appearance of broad charge-transfer (CT) absorption bands upon addition of EAs to solutions of RTILs in acetonitrile (2). These broad bands reveal the formation of ground-state electron donor-acceptor (EDA) complexes between the anions of the RTILs and the EAs. TA measurements from fs to ns, showed that, upon CT excitation, the radical of the RTIL anion is formed which can accept an electron from D. This does not only explain the peculiar observations but also describes a pathway for RTIL photo-degradation since the redox reaction is not completely reversible.

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Eric Vauthey

Physical Chemistry Department - Sciences II - University of Geneva
30, Quai Ernest Ansermet - CH-1211 Geneva 4 (Switzerland)

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