The interaction between hexahydroxytriphenylene and the rutile TiO2(110)-(1 x 1) surface at UHV conditions

The interaction between 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and the ruble TiO2(110)-(1 x 1) surface under ultrahigh vacuum (UHV) conditions was investigated using X-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and density functional theory (DFT) calculations. The NEXAFS results showed that HHTP molecules formed a submonolayer and a monolayer that aligned along the [001]-direction with, respectively, a more or less flat downward orientation and a more upright orientation to the TiO2 surface. The HHTP molecules that aligned along the [001]-direction were most likely grafted onto the TiO2(110) surface by a bidentate bridge between each of the oxygen atoms of one of the catechol units within the HHTP molecule and two adjacent Ti(5f)(4+) ions on the TiO2(110) surface. The coordination is non-dissociative in the case of the submonolayer, but dissociative in the monolayer, according to the analysis of the C1s XPS, UPS, C1s NEXAFS data and complementary OFT calculations. (C) 2010 Elsevier BM. All rights reserved.