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          Institute: Fritz-Haber-Institut     Collection: Physical Chemistry     Display Documents

ID: 428741.0, Fritz-Haber-Institut / Physical Chemistry
Excitation mechanism in the photoisomerization of a surface-bound azobenzene derivative: Role of the metallic substrate
Authors:Hagen, Sebastian; Kate, Peter; Leyssner, Felix; Nandi, Dhananjay; Wolf, Martin; Tegeder, Petra
Date of Publication (YYYY-MM-DD):2008-10-22
Title of Journal:Journal of Chemical Physics
Journal Abbrev.:J. Chem. Phys.
Issue / Number:16
Start Page:164102–1
End Page:164102–8
Copyright:© 2008 American Institute of Physics
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:Two-photon photoemission (2PPE) spectroscopy is employed to elucidate the electronic structure and the excitation mechanism in the photoinduced isomerization of the molecular switch tetra-tert-butyl-azobenzene (TBA) adsorbed on Au(111). Our results demonstrate that the optical excitation and the mechanism of molecular switching at a metal surface is completely di®erent compared to the corresponding process for the free molecule. In contrast to direct (intramolecular) excitation operative in the isomerization in the liquid phase, the conformational change of the surface-bound TBA is driven by a substrate-mediated charge transfer process. We find, that photoexcitation above a threshold hn ≈2.2 eV leads to hole formation in the Au d-band followed by a hole transfer to the highest occupied molecular orbital (HOMO) of TBA. This transiently formed positive ion resonance subsequently results in a conformational change. The photon energy dependent photoisomerization cross section exhibit an unusual shape for a photochemical reaction of an adsorbate on a metal surface. It shows a threshold like behavior below hn ≈2.2 eV and above hn≈4.4 eV. These thresholds correspond to the minimum energy required to create single or multiple hot holes in the Au d-bands, respectively. This study provides important new insights into the use of light to control the structure and function of molecular switches in direct contact with metal electrodes.
External Publication Status:published
Document Type:Article
Communicated by:Martin Wolf
Affiliations:Fritz-Haber-Institut/Physical Chemistry
External Affiliations:Hagen S, Kate P, Leyssner F, Nandi D, Wolf M, Tegeder P, Freie Univ Berlin, FB Physik, Arnimallee 14, 14195 Berlin, Germany
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