Combined experimental and DFT-TDDFT computational study of photoelectrochemical cell ruthenium sensitizers

We report a combined experimental and computational study of several ruthenium(II) sensitizers originated from the [Ru(dcbpyH₂) ₂(NCS)₂], N3, and [Ru(dcbpyH₂)(tdbpy)(NCS) ₂], N621, (dcbpyH₂ = 4,4′-dicarboxy-2,2′- bipyridine, tdbpy = 4,4′-tridecyl-2,2′-bipyridine) complexes. A purification procedure was developed to obtain pure N-bonded isomers of both types of sensitizers. The photovoltaic data of the purified N3 and N621 sensitizers adsorbed on TiO₂ films in their monoprotonated and diprotonated state, exhibited remarkable power conversion efficiency at 1 sun, 11.18 and 9.57%, respectively. An extensive Density Functional Theory (DFT)-Time Dependent DFT study of these sensitizers in solution was performed, investigating the effect of protonation of the terminal carboxylic groups and of the counterions on the electronic structure and optical properties of the dyes. The calculated absorption spectra are in good agreement with the experiment, thus allowing a detailed assignment of the UV-vis spectral features of the two types of dyes. The computed alignments of the molecular orbitals of the different complexes with the band edges of a model TiO₂ nanoparticle provide additional insights into the electronic factors governing the efficiency of dye-sensitized solar cell devices.