Ruthenium Dyes with Azo Ligands: Light Harvesting, Excited-State Properties and Relevance to Dye-Sensitised Solar Cells

Abstract

A series of new RuII complexes has been synthesised, with different azo ligands as additional chromophore. The dyes are all intensely colored due to MLCT and ILCT transitions in the visible region. The photophysical study of the dyes, carried out by UV/Vis absorption and emission spectroscopy, showed unusual features such as intense solvatochromism and solvent-dependent extinction coefficients. The energies of these excited states have been tuned by changing the electron density across the series of azo ligands, and this results in different contributions from each charge transfer process for the different complexes and consequently, different emission behavior. The detailed behaviour of these dyes was further studied and interpreted through electrochemical, structural and computational techniques. The dyes do not work well as sensitisers for DSSCs and this is investigated by emission spectroscopy on TiO2 and ZrO2 films, suggesting poor charge injection to TiO2.