Electron Turnstile

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Science  27 Aug 2010:
Vol. 329, Issue 5995, pp. 997
DOI: 10.1126/science.329.5995.997-d

In artificial photosynthetic models, propelling excited electrons forward rather than backward can prove challenging. Meylemans et al. have designed a small molecular complex that elegantly tilts the odds toward forward progression by virtue of the cant of a single phenyl ring. The ring bridges a ruthenium ligand to a viologen acceptor, and tilts to varying degrees out-of-plane depending on its substitution pattern. Upon visible light absorption by the ruthenium center, the resulting excited state favors a lower cant angle, which facilitates electron transfer to the viologen through pi conjugation. After the transfer event, however, steric factors once again dominate, tilting the bridging ring back to inhibit the electron's return to the metal. Increasing the steric demand of the phenyl ring's subtituents raised the ratio of forward to reverse charge transfer rates from ∼3 to 14.

J. Am. Chem. Soc. 132, 10.1021/ja1055559 (2010).

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