Protonation-Dependent Binding of Ruthenium Bipyridyl Complexes to the Anatase(101) Surface

Abstract

In dye sensitized solar cells, three structurally similar dyes are commonly employed to sensitize anatase nano-crystals, namely the cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)-ruthenium(II) dye (N3), its twice deprotonated (N719) and completely deprotonated (N712) form. Using density functional theory, several possible binding geometries of these dyes are identified on the anatase(101) surface. Computed relative energies show that protonation of the surface can strongly influence the relative stabilities of these configurations, and could induce a conformational transition from double bidentate-bridged binding to mixed bidentate/monodentate binding. Attenuated total reflection (ATR)-IR experiments and computed vibrational spectra provide additional support for a protonation dependent equilibrium between two different configurations. Furthermore, self-assembly in chains of hydrogen bonded dye molecules seems structurally favorable on the anatase(101) surface, for enantiopure dyes a packing density of 0.744/nm 2 could be achieved.

In situ investigation of dye adsorption on TiO2 films using a quartz crystal microbalance with a dissipation technique

“…15,16 The rest of the TiO 2 underneath the dye will remain covered with solvent molecules. 17 Moreover, MeCN molecules may be replaced by t BuOH molecules, which will not change the area weight. The observed frequency shift during exposure is due to simultaneous bulk viscosity change and dye adsorption.…”

In Situ Mapping of the Molecular Arrangement of Amphiphilic Dye Molecules at the TiO2 Surface of Dye-Sensitized Solar Cells

“…Fourier transform infrared spectroscopy was successfully used to observe the binding of dye molecules to the TiO 2 surface of DSCs. 9,13 The average orientation of adsorbed molecules relative to the surface could be derived from combined near-edge x-ray absorption fine structure spectroscopy (NEXAFS) and photoelectron spectroscopy (PES). [14][15][16] However, the irregular mesoporous titania surface prevents averaging techniques from capturing 4 local molecular details.…”

First Principle Modelling of Materials and Processes in Dye-Sensitized Photoanodes for Solar Energy and Solar Fuels

“…Finally, the sensitizer's grafting group should establish a stable binding of the dye onto the metal oxide surface, thus ensuring long-term stability of the cell [163][164][165]. Investigation of the adsorption of organic dyes onto TiO 2 cluster models [161,162,166], has largely shown that the bidentate bridging adsorption mechanism with proton transfer to a nearby surface oxygen is the energetically favored one (Figure 6), while the monodentate anchoring is usually predicted to be less stable, although some dependency on the employed methodology can be outlined [166], For Ru(II) sensitizers different adsorption modes onto the TiO 2 surface can be found: while homoleptic dyes, such as N3 or N719, can adsorb on TiO 2 using carboxylic anchoring groups residing on different bipyridine ligands and hence using up to three carboxylic groups (Figure 6c) [159,167], heteroleptic dyes, e.g., N621, C106, or Z907, necessarily adsorb via carboxylic groups residing on the same bipyridine (two carboxylic groups, Figure 6d) [168,169].…”