Bis-Cyclometalated Iridium Complexes Containing 4,4 '-Bis(Phosphonomethyl)-2,2 '-Bipyridine Ligands: Photophysics, Electrochemistry, And High-Voltage Dye-Sensitized Solar Cells

In this report, the synthesis and characterization of two bis-cyclometalated iridium(III) complexes are presented. Single-crystal X-ray diffraction shows that [Ir(ppy)(2)(4,4'-bis-diethylphosphonomethyl)-2,2'-bipyridine)]PF6 adopts a pseudooc-tahedral geometry. The complexes have an absorption feature in the near-visible-UV region and emit green light with excited-state lifetimes in hundreds of nanoseconds. The redox properties of these complexes show reversible behavior for both oxidative and reductive events. [Ir(ppy)(2)(4,4'-bis(phosphonomethyl)-2,2'-bipyridine)]PF6 readily binds to metal oxide supports, like nanostructured Se-doped In2O3 and TiO2, while still retaining reversible redox chemistry. When incorporated as the photoanode in dye-sensitized solar cells, the devices exhibit open-circuit voltages of >1 V, which is a testament to their strength of these iridium(III) complexes as photochemical oxidants.