We investigate the ultrafast transient absorption response of tetrakis(μ-pyrophosphito)diplatinate(II), [Pt2(μ-P2O5H2)4]4- [hereafter abbreviated Pt(pop)], in acetonitrile upon excitation of its lowest singlet 1A2u state. Compared with previously reported solvents [van der Veen RM, Cannizzo A, van Mourik F, Vlček A, Jr, Chergui M (2011) J Am Chem Soc 133:305-315], a significant shortening of the intersystem crossing (ISC) time (<1 ps) from the lowest singlet to the lowest triplet state is found, allowing for a transfer of vibrational coherence, observed in the course of an ISC in a polyatomic molecule in solution. Density functional theory (DFT) quantum mechanical/molecular mechanical (QM/MM) simulations of Pt(pop) in acetonitrile and ethanol show that high-lying, mostly triplet, states are strongly mixed and shifted to lower energies due to interactions with the solvent, providing an intermediate state (or manifold of states) for the ISC. This suggests that the larger the solvation energies of the intermediate state(s), the shorter the ISC time. Because the latter is smaller than the pure dephasing time of the vibrational wave packet, coherence is conserved during the spin transition. These results underscore the crucial role of the solvent in directing pathways of intramolecular energy flow.

Beckman Institute California Institute of Technology Pasadena CA 91125

J Heyrovský Institute of Physical Chemistry Czech Academy of Sciences CZ 182 23 Prague Czech Republic

Laboratoire de Spectroscopie Ultrarapide Lausanne Centre for Ultrafast Science Institut des Sciences et Ingénierie Chimiques School of Basic Sciences Ecole Polytechnique Fédérale de Lausanne CH 1015 Lausanne Switzerland

Laboratoire de Spectroscopie Ultrarapide Lausanne Centre for Ultrafast Science Institut des Sciences et Ingénierie Chimiques School of Basic Sciences Ecole Polytechnique Fédérale de Lausanne CH 1015 Lausanne Switzerland;

School of Biological and Chemical Sciences Queen Mary University of London London E1 4NS United Kingdom

Science and Technology Department IBM Research GmbH Zurich Research Laboratory 8803 Rüschlikon Switzerland

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