Anchoring ligands and their ruthenium(II) complexes as sensitizers for titanium dioxide solar cells

A series of substituted 2,6-di-(4'-carboxyquinolin-2'-yl)pyridine and 4,4'-dicarboxy-2,2'-biquinoline derivatives as anchoring ligands was synthesized by utilizing the Pfitzinger reaction. This approach was ineffective when the precursor isatin contains strong electron-withdrawing groups. The photo- and electrochemistry of complexes of these ligands with Ru(II) and Cu(I) was investigated. Despite the different substituent electronegativities no dramatic differences were observed in the electronic absorption properties for these complexes. However, oxidation potentials were found to increase as the ligands became more electronegative.; A series of di-(quninol-2'-yl) and di-(pyrid-2'-yl) derivatives of pyrimidine and pyridazine was synthesized as bridging ligands for Ru(II) by utilizing the Pfitzinger and Stille coupling reactions, and the photo- and electrochemistry of the mono-nuclear Ru(II) complexes of these ligands was investigated. The photovoltaic performance of thin films of anatase TiO2 impregnated with the Ru(II) complexes of 102b and 103b was evaluated using a solution of I-/I3- in acetonitrile as the electron mediator. The energy levels of the oxidized form and the excited state of these sensitizers are favorable for the oxidation of I- in the electrolyte solution and the injection of an electron into the conduction band of TiO2. The complexes show broad and intense absorption throughout visible region. The non-choromophoric thiocyanate ligand (NCS) helps to increase IPCE at the longer wavelengths.; Using a Friedlander condensation approach, a series of 2-(pyrid-2'-yl)-1,8-naphthyridines containing a carboethoxy group appended at the 4- and/or 4'-positions was prepared. Complexation of these ligands with Ru(II) and NaNCS led to the complexes [Ru(L)2(NCS)2] and subsequent hydrolysis of the ester groups afforded the carboxylic acid dyes [Ru(114-116b)2 (NCS)2]. Unlike the other unsymmetrical bidentate ligands such as 65a and 128, pyridylnaphthyridine ligands 114a-116a stereoselectively formed octahedral Ru(II) complexes. The complexes have broad and intense absorption throughout visible region. The more delocalized and electronegative nature of the 1,8-naphthyridyl moiety lowers the energy of the ligand pi*-level and extends the absorption envelope of these complexes well into the red. The system lacking a 4-carboxypyridine moiety shows poor absorbance in the blue region of the spectrum. Solar cells involving thin films of anatase TiO2 impregnated with these dyes were prepared and their photovoltaic performance was evaluated. The incident photon-to-current efficiencies in the region beyond 625 nm were considerably greater than the prototype N3 dye.