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Evidence for Ultralow-Energy Vibrations in Large Organic Molecules

Lookup NU author(s): Dr Thomas Pope, Professor Werner Hofer



This is the authors' accepted manuscript of an article that has been published in its final definitive form by American Chemical Society, 2017.

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The quantum efficiency or the rate of conversionof incident photon to free electron in photosynthesis is knownto be extremely high. It has long been thought that the origin ofthis efficiency are molecular vibrations leading to a very fastseparation of electrons and holes within the involved molecules.However, molecular vibrations are commonly in the range above100 meV, which is too high for excitations in an ambientenvironment. Here, we analyze experimental spectra of singleorganic molecules on metal surfaces at ∼4 K, which often exhibita pronounced dip. We show that measurements on iron(II)[tetra-(pentafluorophenyl)]porphyrin resolve this single dip at 4K into a series of step-shaped inelastic excitations at 0.4 K. Via extensive spectral maps under applied magnetic fields andcorresponding theoretical analysis we find that the dip is due to ultralow-energy vibrations of the molecular frame, typically in therange below 20 meV. The result indicates that ultralow energy vibrations in organic molecules are much more common thancurrently thought and may be all-pervasive for molecules above a certain size.

Publication metadata

Author(s): Chen H, Pope T, Wu Z, Wang D, Tao L, Bao D, Xiao W, Zhang J, Zhang Y, Du S, Gao S, Pantelides ST, Hofer WA, Gao H-J

Publication type: Article

Publication status: Published

Journal: Nano Letters

Year: 2017

Volume: 17

Issue: 18

Pages: 4929-4933

Print publication date: 09/08/2017

Online publication date: 20/07/2017

Acceptance date: 20/07/2017

Date deposited: 15/08/2017

ISSN (print): 1530-6984

ISSN (electronic): 1530-6992

Publisher: American Chemical Society


DOI: 10.1021/acs.nanolett.7b01963


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