On the mechanism of vibrational control of light-induced charge transfer in donor–bridge–acceptor assemblies

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Abstract

Nuclear–electronic (vibronic) coupling is increasingly recognized as a mechanism of major importance in controlling the light-induced function of molecular systems. It was recently shown that infrared light excitation of intramolecular vibrations can radically change the efficiency of electron transfer, a fundamental chemical process. We now extend and generalize the understanding of this phenomenon by probing and perturbing vibronic coupling in several molecules in solution. In the experiments an ultrafast electronic–vibrational pulse sequence is applied to a range of donor–bridge–acceptor Pt(II) trans-acetylide assemblies, for which infrared excitation of selected bridge vibrations during ultraviolet-initiated charge separation alters the yields of light-induced product states. The experiments, augmented by quantum chemical calculations, reveal a complex combination of vibronic mechanisms responsible for the observed changes in electron transfer rates and pathways. The study raises new fundamental questions about the function of vibrational processes immediately following charge transfer photoexcitation, and highlights the molecular features necessary for external vibronic control of excited-state processes.

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Figure 1: Summary of infrared-control experiments.
Figure 2: TRIR and infrared control results for all three molecular systems.
Figure 3: Excited-state dynamics of PTZ-Pt-NAP with and without infrared excitation.
Figure 4: Calculated energies of the CT (triplet, black), CSS (triplet, blue) and 3NAP (triplet, red) states along the NAP side C≡C coordinate in the ground state geometries of the molecules studied, in CH2Cl2.
Figure 5: Measuring the ν(C≡C) IVR rate in different electronic states of OMe-PTZ-Pt-NAP in CH2Cl2.

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Acknowledgements

The authors thank A. Parker and A. Vlcek for discussions. The authors acknowledge the support of the Engineering and Physical Sciences Research Council (EPSRC), the University of Sheffield and the Science and Technology Facilities Council (STFC). Calculations were performed on the local ‘Jupiter’ cluster of the Theoretical Chemistry Group and the central ‘Iceberg’ cluster of the University of Sheffield. A licence for the OpenEye tools was obtained via the free academic licensing programme.

Author information

M.D. and J.A.W. conceived and designed the experiments. M.D., I.V.S. and J.A.W. conducted the experiments on a set-up built and operated by M.T., G.M.G. and I.V.S. M.D. analysed the experimental data. P.A.S. synthesized the molecules. T.K. and A.J.H.M.M. devised, performed and analysed the DFT calculations and considered their correspondence to experimental data. M.D. and J.A.W. wrote the paper, with input from all authors.

Correspondence to Anthony J. H. M. Meijer or Julia A. Weinstein.

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Delor, M., Keane, T., Scattergood, P. et al. On the mechanism of vibrational control of light-induced charge transfer in donor–bridge–acceptor assemblies. Nature Chem 7, 689–695 (2015) doi:10.1038/nchem.2327

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