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  Direct Observation of Photoinduced Tautomerization in Single Molecules at a Metal Surface

Böckmann, H., Liu, S., Mielke, J., Gawinkowski, S., Waluk, J., Grill, L., et al. (2016). Direct Observation of Photoinduced Tautomerization in Single Molecules at a Metal Surface. Nano Letters, 16(2), 1034-1041. doi:10.1021/acs.nanolett.5b04092.

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Böckmann, Hannes1, Author           
Liu, Shuyi1, Author           
Mielke, Johannes1, Author           
Gawinkowski, S.2, Author
Waluk, J.2, 3, Author
Grill, Leonhard1, 4, Author           
Wolf, Martin1, Author           
Kumagai, Takashi1, Author           
Affiliations:
1Physical Chemistry, Fritz Haber Institute, Max Planck Society, ou_634546              
2Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, Warsaw 01-224, Poland, ou_persistent22              
3Faculty of Mathematics and Natural Sciences, College of Science, Cardinal Stefan Wyszynski University, Dewajtis 5, 01-815 Warsaw, Poland, ou_persistent22              
4Universität Graz, ou_persistent22              

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 Abstract: Molecular switches are of fundamental importance in nature, and light is an important stimulus to selectively drive the switching process. However, the local dynamics of a conformational change in these molecules remain far from being completely understood at the single-molecule level. Here, we report the direct observation of photoinduced tautomerization in single porphycene molecules on a Cu(111) surface by using a combination of low-temperature scanning tunneling microscopy and laser excitation in the near-infrared to ultraviolet regime. It is found that the thermodynamically stable trans configuration of porphycene can be converted to the metastable cis configuration in a unidirectional fashion by photoirradiation. The wavelength dependence of the tautomerization cross section exhibits a steep increase around 2 eV and demonstrates that excitation of the Cu d-band electrons and the resulting hot carriers play a dominant role in the photochemical process. Additionally, a pronounced isotope effect in the cross section (∼100) is observed when the transferred hydrogen atoms are substituted with deuterium, indicating a significant contribution of zero-point energy in the reaction. Combined with the study of inelastic tunneling electron-induced tautomerization with the STM, we propose that tautomerization occurs via excitation of molecular vibrations after photoexcitation. Interestingly, the observed cross section of ∼10–19 cm2 in the visible–ultraviolet region is much higher than that of previously studied molecular switches on a metal surface, for example, azobenzene derivatives (10–23–10–22 cm2). Furthermore, we examined a local environmental impact on the photoinduced tautomerization by varying molecular density on the surface and find substantial changes in the cross section and quenching of the process due to the intermolecular interaction at high density.

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 Dates: 2015-12-312015-10-082016-01-212016-02-10
 Publication Status: Issued
 Pages: 8
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1021/acs.nanolett.5b04092
 Degree: -

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Title: Nano Letters
  Abbreviation : Nano Lett.
Source Genre: Journal
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Publ. Info: Washington, DC : American Chemical Society
Pages: - Volume / Issue: 16 (2) Sequence Number: - Start / End Page: 1034 - 1041 Identifier: ISSN: 1530-6984
CoNE: https://pure.mpg.de/cone/journals/resource/110978984570403