Bis-Cyclometalated Iridium Complexes Containing 4,4′-Bis(phosphonomethyl)-2,2′-bipyridine Ligands: Photophysics, Electrochemistry, and High-Voltage Dye-Sensitized Solar Cells

Abstract

In this report, the synthesis and characterization of two bis-cyclometalated iridium(III) complexes are presented. Singlecrystal X-ray diffraction shows that [Ir(ppy) 2 (4,4′-bis-(diethylphosphonomethyl)-2,2′-bipyridine)]PF 6 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)]PF 6 readily binds to metal oxide supports, like nanostructured Sn IV -doped In 2 O 3 and TiO 2 , 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.

A Series of Green Light Absorbing Organic Photosensitizers Capable of Oxidative Quenching Photocatalysis

“…Qualitatively consistent with the energy gap law (i. e. non‐radiative decay rates increase with decreasing energy), the emission quantum yield generally decreases as the emission energy decreases with compounds 1 – 4 (Φ N2 =0.33 to 0.65) all having lower quantum yields than the parent eosin Y (Φ=0.69). None the less, these complexes maintain moderate to high quantum yields that are on average greater than common Ru and Ir polypyridyl photosensitizers [35] …”

“…None the less, these complexes maintain moderate to high quantum yields that are on average greater than common Ru and Ir polypyridyl photosensitizers. [35] Time-resolved emission was measured at the emission maxima of all the complexes and the results are shown in Figures S13-S17. The emission decays were fit with a single exponential function and the resulting lifetimes (τ) are summarized in Table 1.…”

A Panchromatic Cyclometalated Iridium Dye Based on 2-Thienyl-Perimidine

“…Cyclometalated iridium(III) complexes have proved to be the best emitters in phosphorescent organic light-emitting diodes (PHOLED) due to their bright luminescence, appropriate excited state lifetimes, high thermodynamic and kinetic stability, and fine tuneability of the emission color by simple ligand variation [ 1 , 2 ]. These complexes are also considered as effective photocatalysts [ 3 , 4 ] and promising photosensitizers in solar cells [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. Still, for the latter application, the light-harvesting properties of iridium(III) complexes need to be improved by judicious selection of cyclometalating and/or ancillary ligands.…”

Iron Redox Shuttles with Wide Optical Gap Dyes for High‐Voltage Dye‐Sensitized Solar Cells

“…Recently, Fe(bpy) 3 3+/2+ (where bpy is 2,2′‐bipyridine) and wide optical gap dyes have been paired to yield HV‐DSC devices with photovoltage outputs as high as 1.42 V [6a,c,f] . Our prior studies focused on the dye RR9 and Fe(bpy) 3 3+/2+ which results in the highest photovoltage output from a DSC device to the best of our knowledge with undoped TiO 2 (Figure 2).…”