Toward control of electron transfer in donor-acceptor molecules by bond-specific infrared excitation

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Science  19 Dec 2014:
Vol. 346, Issue 6216, pp. 1492-1495
DOI: 10.1126/science.1259995

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Electron transfer (ET) from donor to acceptor is often mediated by nuclear-electronic (vibronic) interactions in molecular bridges. Using an ultrafast electronic-vibrational-vibrational pulse-sequence, we demonstrate how the outcome of light-induced ET can be radically altered by mode-specific infrared (IR) excitation of vibrations that are coupled to the ET pathway. Picosecond narrow-band IR excitation of high-frequency bridge vibrations in an electronically excited covalent trans-acetylide platinum(II) donor-bridge-acceptor system in solution alters both the dynamics and the yields of competing ET pathways, completely switching a charge separation pathway off. These results offer a step toward quantum control of chemical reactivity by IR excitation.

Big impact from a well-placed shake

Since the advent of ultrashort laser pulses, chemists have sought to steer reaction trajectories in real time by setting particular molecular vibrations in motion. Using this approach, Delor et al. have demonstrated a markedly clear-cut influence on electron transfer probabilities along the axis of a platinum complex. The complex comprised donor and acceptor fragments—which respectively give and take electrons upon ultraviolet excitation—bridged together by triply bonded carbon chains linked to the metal center. By selectively stimulating the carbon triple-bond stretch vibration with an infrared pulse, the authors could induce substantial changes in the observed electron transfer pathways between the fragments.

Science, this issue p. 1492

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