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Reversible photoisomerization of an azobenzene-functionalized self-assembled monolayer probed by sum-frequency generation vibrational spectroscopy

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Wagner,  Steffen
Physical Chemistry, Fritz Haber Institute, Max Planck Society;

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Wolf,  Martin
Physical Chemistry, Fritz Haber Institute, Max Planck Society;

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Citation

Wagner, S., Leyssner, F., Kördel, C., Zarwell, S., Schmidt, R., Weinelt, M., et al. (2009). Reversible photoisomerization of an azobenzene-functionalized self-assembled monolayer probed by sum-frequency generation vibrational spectroscopy. Physical Chemistry Chemical Physics, 11(29), 6242-6248. doi:10.1039/b823330f.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0010-F931-1
Abstract
Sum-frequency generation (SFG) vibrational spectroscopy is employed to investigate the reversible, photoinduced trans/cis isomerization of an azobenzene-functionalized self-assembled monolayer (SAM) on a gold substrate. A C≡N marker group at the outer phenyl ring is used as a direct measure of the switching state. The azobenzene unit is connected to the surface by a tripodal linker system with an adamantane core, which results in both a sufficient decoupling of the functional azobenzene unit from the metallic substrate and a free volume to prevent steric hinderance, thus allowing the isomerization process. Optical excitation at 405 nm induces the trans → cis isomerization, whereas light exposure at 470 nm leads to the back reaction. The effective cross sections for the reactions are σeff(cis) = 4 ± 1 × 1018 cm2 at 405 nm (trans → cis) and σeff(trans) = 2.5 ± 0.9 × 1019 cm2 at 470 nm (cis → trans). We propose that the photoisomerization is driven by a direct (intramolecular) electronic excitation of the azobenzene conjugate, analogous to the free molecules in solution.