DOIAbstract
It is known that excitation by visible light of the singlet metal-to-ligand charge-transfer (1MLCT) states of Fe(II) complexes leads to population of the lowest-lying high-spin quintet state (T-5) with unity quantum yield. Here we investigate this so-called spin crossover (SCO) transition in aqueous iron(II) tris(bipyridine). We use pump-probe transient absorption spectroscopy with a high time resolution of <60 fs in the ultraviolet probe range, in which the T-5 state absorbs, and of <40 fs in the visible probe range, in which both the hot MLCT state and the T-5 state absorb. Our results show that the T-5 state is impulsively populated in less than 50 fs, which is the time we measured for the depopulation of the MCLT manifold. We propose th...
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