Effect of Different Anchoring Groups on the Adsorption of Photoactive Compounds on the Anatase (101) Surface

Abstract

The effect of replacing the anchoring carboxylate groups in the Ru(H(2)dcbpy)(2)(NCS)(2) (H(2)dcbpy = 4,4'-dicarboxylic acid-2,2'- bipyridine) photoactive dye was studied by computational density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The main emphasis in the study was to compare a series of attaching groups, including COOH, B(OH)(2), PO(OH)(2), SO(2)(OH), OH, NO(2), and SiCl(3), by the relative adsorption strength and geometry of the sensitizer molecules on the anatase (101) surface. Additionally, the substituent effect on the absorption signals in simulated UV-vis spectra was calculated with isolated dye molecules. Most of the selected substituents produced only small changes in the absorption characteristics of the dyes. However, OH groups were found to show a quite large blue-shift compared to traditional COOH anchor groups in the simulated UV-vis spectra, while NO(2) groups had an opposite effect of red-shifting the signals. On the other hand, although the NO(2) substituents on the bipyridine ligands led to favorable absorption characteristics, the calculated adsorption strength of the NO(2)-substituted bipyridine models on the surface of anatase (101) was much smaller than that of the COOH-substituted one, indicating that larger modifications are necessary for both attaching the dye molecules on the surface and for tuning the absorption properties of photoactive compounds in the DSSC applications. The computational methods utilized here proved to be an efficient tool to study the effect of subtle structural changes on the properties of the dye molecules.