(472a) New Polypyridyl Ruthenium(II) Sensitizers Carrying Triphenylamine Units and Their Application in Dye Sensitized Solar Cells

Dye sensitized solar cells(DSSC) are composed of nanocrystalline semiconductor oxide film electrodes, dye sensitizers, electrolytes, counter electrodes. In these cells the dye sensitizer is one of the key components for high power conversion efficiency. Dye harvests the sunlight to form excited state and injects electron into the conduction band of the oxide film electrode.Compounds with triphenylamine(TPA) units are widely used organic photosensitizers for their excellent donate electron ability and large conjugation planes that enlarge dyes absorption to visible light. Theoretical and experimental studies have demonstrated that TPA unit suppresses the dye aggregation for its nonplanar structure. In this work, we designed a class of ruthenium photosensitizers endowed with ancillary ligands consisting of TPA units which can enhance light absorption and hole transporting resulting in high photovoltaic efficiency. By Wittig-Horner reaction, TPA segment attaching methyl and methoxy was linked to bipyridine with ethylene or butadiene bridge to form symmetry or asymmetry ligands and characterized by MS, 1H NMR and 13C NMR. Introduction of methoxy increases the solubility of ligands and dyes. Absorption and fluorescence spectrums show that max absorption at 409-430nm and molar extinction coefficient at 3.1-9.0(103m2mol-1), max emission at 509-574nm, fluorescence lifetime at 1.8-4.0ns and fluorescence quantum yield at 11.8-38.4%. According to spectrum data, inserting butadiene bridge between TPA and bipyridine red shifts the max absorption and emission to visible light but decreasing the fluorescence lifetime than inserting ethylene bridge. To insight the relation of ligands structure and dye performance, quantum chemistry data was calculated on Gaussian03 by Hartree-Fock method on 6-31G basis. Calculation result reveals that symmetry and methoxy TPA ligands have bigger dipole moment than asymmetry and methoxy ligands therefore better nonplanar structure and suppressing dyes aggregation on semiconductor oxide surface. Considering the absorption ability and structure character of ligands, TPA ligands with symmetry and methoxy structure are fit to be synthesized dye photosensitizers. Dyes were prepared according to recently developed one-pot synthetic procedure, ligands react with dichloro(p-cymene)ruthenium(II) dimer at 70°C about 4h, with 4,4'-dicarboxy-2,2'-bipyridyl at 150°C about another 4h, finally with KNCS at 150°C about 4h. Related characterizing and testing are processing and absorption spectrums show dyes max absorption at about 530nm and extinction coefficient exceeding 2.4(103m2mol-1) therefore the class of TPA bridging bipyridine ruthenium(II) dyes may have promising performance.