Bis-Cyclometalated Iridium Complexes Containing 4,4′-Bis(phosphonomethyl)-2,2′-bipyridine Ligands: Photophysics, Electrochemistry, and High-Voltage Dye-Sensitized Solar Cells
M. Victoria Bobo, Avishek Paul, Alex J. Robb, Ashley Arcidiacono, Mark D. Smith, Kenneth Hanson, Aaron K. Vannucci
Abstract
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 pseudooctahedral 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 SnIV-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.