Kekulene: On-Surface Synthesis, Orbital Structure, and Aromatic Stabilization

ACS Nano, vol. 14, pp. 15766–15775

Abstract

We revisit the question of kekulene's aromaticity by focusing on the electronic structure of its frontier orbitals as determined by angle-resolved photoemission spectroscopy. To this end, we have developed a specially designed precursor, 1,4,7(2,7)-triphenanthrenacyclononaphane-2,5,8-triene, which allows us to prepare sufficient quantities of kekulene of high purity directly on a Cu(111) surface, as confirmed by scanning tunneling microscopy. Supported by density functional calculations, we determine the orbital structure of kekulene's highest occupied molecular orbital by photoemission tomography. In agreement with a recent aromaticity assessment of kekulene based solely on C-C bond lengths, we conclude that the π-conjugation of kekulene is better described by the Clar model rather than a superaromatic model. Thus, by exploiting the capabilities of photoemission tomography, we shed light on the question which consequences aromaticity holds for the frontier electronic structure of a π-conjugated molecule.

Authors 22

1. Anja Haags Aachen Experimentalphysik IV A

   Forschungszentrum Jülich · Jülich Aachen Research Alliance · RWTH Aachen University

   Affiliation as printed

   Experimentalphysik IV A, RWTH Aachen University , ,

   Forschungszentrum Jülich , , ,

   Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology , ,

   Experimentalphysik IV A, RWTH Aachen University, 52074 Aachen, Germany

   Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology, 52425 Jülich, Germany

   Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany

2. Alexander Reichmann

   University of Graz · Nawi Graz

   Affiliation as printed

   Institut für Physik, Karl-Franzens-Universität Graz, NAWI Graz , ,

   Institut für Physik, Karl-Franzens-Universität Graz, NAWI Graz, 8010 Graz, Austria

3. Qitang Fan

   Philipps University of Marburg

   Affiliation as printed

   Philipps-Universität Marburg , , Hans-Meerwein-Str. 4 , ,

   Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Str. 4, 35032 Marburg, Germany

4. Larissa Egger

   University of Graz · Nawi Graz

   Affiliation as printed

   Institut für Physik, Karl-Franzens-Universität Graz, NAWI Graz , ,

   Institut für Physik, Karl-Franzens-Universität Graz, NAWI Graz, 8010 Graz, Austria

5. Hans Kirschner

   Physikalisch-Technische Bundesanstalt

   Affiliation as printed

   Physikalisch-Technische Bundesanstalt (PTB) , ,

   Physikalisch-Technische Bundesanstalt (PTB), 10587 Berlin, Germany

6. Tim Naumann

   Philipps University of Marburg

   Affiliation as printed

   Philipps-Universität Marburg , , Hans-Meerwein-Str. 4 , ,

   Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Str. 4, 35032 Marburg, Germany

7. Simon Werner

   Philipps University of Marburg

   Affiliation as printed

   Philipps-Universität Marburg , , Hans-Meerwein-Str. 4 , ,

   Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Str. 4, 35032 Marburg, Germany

8. Tobias Vollgraff

   Philipps University of Marburg

   Affiliation as printed

   Philipps-Universität Marburg , , Hans-Meerwein-Str. 4 , ,

   Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Str. 4, 35032 Marburg, Germany

9. Jörg Sundermeyer

   Philipps University of Marburg

   Affiliation as printed

   Philipps-Universität Marburg , , Hans-Meerwein-Str. 4 , ,

   Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Str. 4, 35032 Marburg, Germany

10. Lukas Eschmann

    University of Münster

    Affiliation as printed

    Westfälische Wilhelms-Universität Münster , , ,

    Institut für Festkörpertheorie, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany

11. Xiaosheng Yang Aachen Experimentalphysik IV A

    Forschungszentrum Jülich · Jülich Aachen Research Alliance · RWTH Aachen University

    Affiliation as printed

    Experimentalphysik IV A, RWTH Aachen University , ,

    Forschungszentrum Jülich , , ,

    Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology , ,

    Experimentalphysik IV A, RWTH Aachen University, 52074 Aachen, Germany

    Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology, 52425 Jülich, Germany

    Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany

12. Dominik Brandstetter

    University of Graz · Nawi Graz

    Affiliation as printed

    Institut für Physik, Karl-Franzens-Universität Graz, NAWI Graz , ,

    Institut für Physik, Karl-Franzens-Universität Graz, NAWI Graz, 8010 Graz, Austria

13. François C. Bocquet

    Forschungszentrum Jülich · Jülich Aachen Research Alliance

    Affiliation as printed

    Forschungszentrum Jülich , , ,

    Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology , ,

    Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology, 52425 Jülich, Germany

    Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany

14. Georg Koller

    University of Graz · Nawi Graz

    Affiliation as printed

    Institut für Physik, Karl-Franzens-Universität Graz, NAWI Graz , ,

    Institut für Physik, Karl-Franzens-Universität Graz, NAWI Graz, 8010 Graz, Austria

15. Alexander Gottwald

    Physikalisch-Technische Bundesanstalt

    Affiliation as printed

    Physikalisch-Technische Bundesanstalt (PTB) , ,

    Physikalisch-Technische Bundesanstalt (PTB), 10587 Berlin, Germany

16. M. Richter

    Physikalisch-Technische Bundesanstalt

    Affiliation as printed

    Physikalisch-Technische Bundesanstalt (PTB) , ,

    Physikalisch-Technische Bundesanstalt (PTB), 10587 Berlin, Germany

17. Michael G. Ramsey

    University of Graz · Nawi Graz

    Affiliation as printed

    Institut für Physik, Karl-Franzens-Universität Graz, NAWI Graz , ,

    Institut für Physik, Karl-Franzens-Universität Graz, NAWI Graz, 8010 Graz, Austria

18. Michael Rohlfing corresponding

    University of Münster

    Affiliation as printed

    Westfälische Wilhelms-Universität Münster , , ,

    Institut für Festkörpertheorie, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany

19. Peter Puschnig corresponding

    University of Graz · Nawi Graz

    Affiliation as printed

    Institut für Physik, Karl-Franzens-Universität Graz, NAWI Graz , ,

    Institut für Physik, Karl-Franzens-Universität Graz, NAWI Graz, 8010 Graz, Austria

20. J. Michael Gottfried corresponding

    Philipps University of Marburg

    Affiliation as printed

    Philipps-Universität Marburg , , Hans-Meerwein-Str. 4 , ,

    Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Str. 4, 35032 Marburg, Germany

21. Serguei Soubatch corresponding

    Forschungszentrum Jülich · Jülich Aachen Research Alliance

    Affiliation as printed

    Forschungszentrum Jülich , , ,

    Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology , ,

    Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology, 52425 Jülich, Germany

    Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany

22. Frank Stefan Tautz Aachen Experimentalphysik IV A

    Forschungszentrum Jülich · Jülich Aachen Research Alliance · RWTH Aachen University

    Affiliation as printed

    Experimentalphysik IV A, RWTH Aachen University , ,

    Forschungszentrum Jülich , , ,

    Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology , ,

    Experimentalphysik IV A, RWTH Aachen University, 52074 Aachen, Germany

    Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology, 52425 Jülich, Germany

    Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany