Photoemission Study of Azobenzene and Aniline Adsorbed on TiO_{2} Anatase (101) and Rutile (110) Surfaces

Abstract

ABSTRACT: 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 #at-lying molecule into two upright phenyl imide species. An irradiation-induced trans!cis isomer conversion is proposed to facilitate the azobenzene cleavage. These results con"rm that the NdN double bond of azobenzene is cleaved by TiO2 in the fullcoverage 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 T aniline conversion at TiO2 surfaces [Li, S.-C.; Diebold, U. J. Am. Chem. Soc. 2010, 132, 64].