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Quantum chemistry

A lightning-fast change

Nature Physics volume 8, pages 179–180 (2012)Cite this article

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A single photon can alter the shape of a molecule. It is now shown that quantum effects can play an important role in this change leading to conformation relaxation rates hundreds of times faster than previously expected.

Conformational relaxation is one of the most common photophysical processes that occur in large conjugated molecules upon photoexcitation; bond angles and lengths adjust to a new excited-state geometry in a motion that is typically overdamped by friction. Jenny Clark and her colleagues, reporting in Nature Physics1, have now discovered that, under the right circumstances, such torsional reorganization can be ultrafast, occurring in less than a vibrational period — two orders of magnitude faster than is typical for such motion. The authors used a pump–probe technique: an oligofluorene molecule in solution was pumped by a femtosecond laser into a specific electronic state. The changes in absorption for a second probe pulse sent at a variable delay were then used to monitor the flattening dynamics of the molecular structure. The torsional mode responsible for these dynamics was pumped by electronic relaxation following the optical excitation and acquires high energy in a short time scale (100 fs), which induces an inertial, frictionless motion that results in a large configurational change.

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  1. Shaul Mukamel is in the Department of Chemistry, University of California, Irvine, California 92697-2025, USA,

    Shaul Mukamel

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  1. Shaul Mukamel
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Correspondence to Shaul Mukamel.

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Mukamel, S. A lightning-fast change. Nature Phys 8, 179–180 (2012). https://doi.org/10.1038/nphys2226

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