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Direct observation of photoinduced tautomerization in single molecules at a metal surface

  • 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 pronouncedMolecular 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.zeige mehrzeige weniger

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Metadaten
Autoren/innen:H. Böckmann, S. Liu, Johannes Mielke, S. Gawinkowski, J. Walluk, L. Grill, M. Wolf, T. Kumagai
Dokumenttyp:Zeitschriftenartikel
Veröffentlichungsform:Verlagsliteratur
Sprache:Englisch
Titel des übergeordneten Werkes (Englisch):Nano Letters
Jahr der Erstveröffentlichung:2016
Organisationseinheit der BAM:6 Materialchemie
6 Materialchemie / 6.1 Oberflächenanalytik und Grenzflächenchemie
Verlag:ACS
Jahrgang/Band:16
Ausgabe/Heft:2
Erste Seite:1034
Letzte Seite:1041
DDC-Klassifikation:Naturwissenschaften und Mathematik / Chemie / Analytische Chemie
Freie Schlagwörter:Pophycene; STM
Themenfelder/Aktivitätsfelder der BAM:Analytical Sciences
Analytical Sciences / Oberflächen- und Grenzflächenanalytik
DOI:https://doi.org/10.1021/acs.nanolett.5b04092
ISSN:1530-6984
ISSN:1530-6992
Verfügbarkeit des Dokuments:Datei im Netzwerk der BAM verfügbar ("Closed Access")
Datum der Freischaltung:22.04.2016
Referierte Publikation:Ja
Datum der Eintragung als referierte Publikation:26.04.2016