Photoemission study of azobenzene and aniline adsorbed on TiO2 anatase (101) and rutile (110) surfaces

S.-C. Li1, Y. Losovyj2, V.K. Paliwal1,3, U. Diebold1,4

1 Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana 70118, U.S.A.
2 Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, Louisiana 70806, U.S.A.
3 Department of Physics, Dyal Singh College, Lodhi Road, New Delhi-110003, India
4 Institut für Angewandte Physik, Technische Universität Wien, 1040 Wien, Austria

J. Phys. Chem. C 115 (2011) 10173-10179

The electronic structure of azobenzene and aniline, adsorbed on two TiO2 surfaces, anatase (101) and rutile (110), has been studied with ultraviolet synchrotron-based photoemission spectroscopy (UPS). At saturation coverage, azobenzene and aniline exhibit very similar molecular orbitals in UPS valence band spectra. Angle-resolved UPS exhibits anisotropy of the molecular states along the polar and azimuthal direction, as is expected for highly oriented superstructures. For a low coverage of azobenzene adsorbed on anatase, photon irradiation results in the conversion of the flat-lying molecule into two upright phenyl imide species. An irradiation-induced trans-cis isomer conversion is proposed to facilitate the azobenzene cleavage. These results confirm that the N=N double bond of azobenzene is cleaved by TiO2 in the full-coverage regime and that the resulting intermediate is bonded to the substrate, in agreement with a previous scanning tunneling microscopy study and a proposed reaction scheme for azobenzene <-> aniline conversion at TiO2 surfaces [Li, S.-C.; Diebold, U. J. Am. Chem. Soc. 2010, 132, 64].

Corresponding author: U. Diebold (diebold at iap_tuwien_ac_at).

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