highlight 12 2018

We wish to understand the nature of ion pairs - the product in bimolecular photoinduced charge separation (CS). We are exploring whether there is a spectral signature in the excited-state dynamics of these species that reports on the dissociation of ion pairs into free ions. We accomplish this using pump-pump-probe (PPP) spectroscopy. The first pump pulse triggers a CS and, after a defined time delay, Δt12, a transient electronic absorption measurement is carried out on the ensuing ion population. In the PPP spectrum at time zero, the intensity of the red feature decreases with Δt12, whilst the blue feature increases. If one normalises this to the bleach (the negative feature that corresponds to the anion absorption band in top spectrum), these appear exponential with Δt12, as one would expect if these features tracked the distance distribution. This for the first time gives us clear, specific spectral signatures of the changes in the ion pair distribution.

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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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