Adsorption of bi-isonicotinic acid on rutile TiO2(110)

Abstract

Bi-isonicotinic acid (2,2′-bipyridine–4,4′-dicarboxylic acid) is the ligand of several organometallic dyes, used in photoelectrochemical applications. Therefore the atomic scale understanding of the bonding of this molecule to rutile TiO2(110) should give insight into the crucial dye–surface interaction. High resolution x-ray photoelectron spectroscopy (XPS), near edge x-ray absorption fine structure (NEXAFS), and periodic intermediate neglect of differential overlap (INDO) calculations were carried out on submonolayer bi-isonicotinic acid rutile TiO2(110). Data from multilayers is also presented to support the submonolayer results. For a multilayer, XPS shows that the carboxyl groups remain in the (pristine) protonated form, and NEXAFS show that the molecular plane is tilted by 57° with respect to the surface normal. For the submonolayer, the molecule bonds to the rutile TiO2(110) surface via both deprotonated carboxyl groups, with a tilt angle of 25°, and additionally an azimuthal orientation of 44° with respect to the [001] crystallographic direction. The adsorbant system was also investigated by quantum mechanical calculations using a periodic INDO model. The most stable theoretical adsorption geometry involves a twist around the molecular axis, such that the pyridine rings are tilted in opposite directions. Both oxygen atoms of each carboxyl group are bonded to five-fold coordinated Ti atoms (2M-bidentate), in excellent agreement with the experimental results.

Atomistic simulations of a solid/liquid interface: a combined force field and first principles approach to the structure and dynamics of acetonitrile near an anatase surface

“…[6,7,8,9,10,11] Other workers have employed a slab geometry for the semiconductor, and have investigated electronic properties or binding affinities of model compounds and organic dyes at these surfaces. [12,13,14,15] The computational cost of describing large slabs of TiO 2 has so far prohibited the study of the larger transition metal dyes on the surface. To the best of our knowledge, none of the atomistic studies performed so far takes the solvent, or even better the electrolyte, explicitly into account.…”

Exploring ultra-fast charge transfer and vibronic coupling with N 1s RIXS maps of an aromatic molecule coupled to a semiconductor

“…The LUMO+1 observed at 400.2 eV for the monolayer is derived from the adsorption bond and has previously been observed both experimentally and computationally for a biisonicotinic acid monolayer on the rutile TiO 2 (110) surface. 7 The interpretation of the monolayer RIXS is largely the same as for the multilayer, with features below 396 eV emission energy attributed to inelastic scattering, and those above to the elastic scattering. The broad intensity around the elastic line at the LUMO resonance is again attributed to vibronic coupling within the molecule in the core-excited state.…”

“…1). 7 The thickness of the multilayer films is estimated from the XPS to be around 10 nm. Due to the increased penetration depth of x-rays compared to photoelectrons, there will be a small contribution of the first monolayer in the multilayer RIXS measurements.…”

Interplay of adsorbate-adsorbate and adsorbate-substrate interactions in self-assembled molecular surface nanostructures

“…6(d)), leads first to the reduction, followed by the disappearance of the higher binding energy component. This kind of modification of the O 1s line shape is typical for a deprotonation reaction of carboxylic groups concomitant with the formation of a covalent bond between the substrate and the carboxylate [16,20]. It can be explained by the presence of two inequivalent oxygen species in the protonated molecule, which are rendered equivalent by deprotonation and bond formation.…”