Long‐Distance Rate Acceleration by Bulk Gold

• Published in: Angewandte Chemie International Edition Vol. 58; no. 20; pp. 6574 - 6578
• Main Authors: Schlimm, Alexander, Löw, Roland, Rusch, Talina, Röhricht, Fynn, Strunskus, Thomas, Tellkamp, Tobias, Sönnichsen, Frank, Manthe, Uwe, Magnussen, Olaf, Tuczek, Felix, Herges, Rainer
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 13.05.2019; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Acceleration; azobenzene; Catalysis; Chemistry; Chemistry, Multidisciplinary; Coupling (molecular); Density distribution; Gold; Isomerization; Kinetics; Physical Sciences; Reaction kinetics; Science & Technology; self-assembled monolayers; surface spectroscopy; vibrational spectroscopy; azobenzene; PHOTOISOMERIZATION; MOLECULE; catalysis; PLATFORM; AU; SPECTROSCOPY; CIS-TRANS ISOMERIZATION; KINETICS; vibrational spectroscopy; surface spectroscopy; TRIAZATRIANGULENIUM ADLAYERS; self-assembled monolayers; SURFACES
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201814342

We report on a very unusual case of surface catalysis involving azobenzenes in contact with a Au(111) surface. A rate acceleration of the cis–trans isomerization on gold up to a factor of 1300 compared to solution is observed. By using carefully designed molecular frameworks, the electronic coupling to the surface can be systematically tuned. The isomerization kinetics of molecules with very weak coupling to the metal is similar to that found in solution. For their counterparts with strong coupling, the relaxation rate is shown to depend on the spin‐density distribution in the triplet states of the molecules. This suggests that an intersystem crossing is involved in the relaxation process. Aside from their impact on catalytic processes, these effects could be used to trigger reactions over long distances. Remote control: Azobenzenes standing upright on a gold surface isomerize from cis to trans faster than in solution, by several orders of magnitude. A coupling unit allows to tune between those extremes. Experimental and theoretical investigations show that the 1300‐fold rate acceleration is due to a singlet–triplet–singlet spin change, which is forbidden in solution but mediated by bulk gold over 11 bonds and a distance of 14 Å.