Directing the path of light-induced electron transfer at a molecular fork using vibrational excitation


Ultrafast electron transfer in condensed-phase molecular systems is often strongly coupled to intramolecular vibrations that can promote, suppress and direct electronic processes. Recent experiments exploring this phenomenon proved that light-induced electron transfer can be strongly modulated by vibrational excitation, suggesting a new avenue for active control over molecular function. Here, we achieve the first example of such explicit vibrational control through judicious design of a Pt(II)-acetylide charge-transfer donor–bridge–acceptor–bridge–donor ‘fork’ system: asymmetric 13C isotopic labelling of one of the two –C≡C– bridges makes the two parallel and otherwise identical donor→acceptor electron-transfer pathways structurally distinct, enabling independent vibrational perturbation of either. Applying an ultrafast UVpump(excitation)–IRpump(perturbation)–IRprobe(monitoring) pulse sequence, we show that the pathway that is vibrationally perturbed during UV-induced electron transfer is dramatically slowed down compared to its unperturbed counterpart. One can thus choose the dominant electron transfer pathway. The findings deliver a new opportunity for precise perturbative control of electronic energy propagation in molecular devices.

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Figure 1: Summary of the multipulse IR-control experiments.
Figure 2: Ground-state infrared absorption properties of 1* in CD2Cl2.
Figure 3: Summary of excited-state dynamics with and without vibrational perturbation in CH2Cl2, with the middle panel showing results for ν(13C) excitation and the right panel for ν(12C) excitation (2,016 and 2,104 cm−1, respectively).
Figure 4: Modelling of the kinetic evolution of the off-diagonal response in IR-control experiments.


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Financial support of the EPSRC, the E-Futures Doctoral Training Centre, the University of Sheffield, and the STFC, including access to beam time, is gratefully acknowledged. We thank A. W. Parker for inspiring discussions, and E. Greenough, G. Farrow, A. Auty, and A. Sadler for help with variable temperature measurements.

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M.D. and J.A.W. conceived the hypothesis; M.D., I.V.S. and J.A.W. designed the experiments; M.D., S.A.A. and I.V.S. 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; S.A.A. synthesized the molecules; T.K. and A.J.H.M.M. performed supporting DFT calculations; M.D. and J.A.W. wrote the paper, with input from all authors.

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Correspondence to Milan Delor or Julia A. Weinstein.

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Delor, M., Archer, S., Keane, T. et al. Directing the path of light-induced electron transfer at a molecular fork using vibrational excitation. Nature Chem 9, 1099–1104 (2017).

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