Spacer and anchor effects on the electronic coupling in ruthenium-bis-terpyridine dye-sensitized TiO2 nanocrystals studied by DFT.

Structural and electronic properties of TiO2 nanoparticles sensitized with a set of Ru(II)(tpy)2 based dyes have been investigated using density functional theory (DFT) calculations combined with time-dependent (TD) DFT calculations. The effects of carboxylic and phosphonic acid anchor groups, as well as a phenylene spacer group, on the optical properties of the dyes and the electronic interactions in the dye-sensitized TiO2 nanoparticles have been investigated. Inclusion of explicit counterions in the modeling shows that the description of the environment is important in order to obtain a realistic interfacial energy level alignment. A comparison of calculated electronic coupling strengths suggests that both the nature of the anchor group and the inclusion of the phenylene spacer group are capable of significantly influencing electron-transfer rates across the dye-metal oxide interface.