Synthesis and characterization of iridium polypyridyl complexes with ester groups with potential applications in covalent attachment to metal oxide surfaces

Abstract

We report the synthesis and characterization of two iridium polypyridyl complexes, [Ir(deeb)₂Cl₂](PF₆) and [Ir(deeb)₂(dpp)](PF₆)₃, where deeb = diethyl-2,2′-bipyridine-4,4′-dicarboxylate and dpp = 2,3-bis(2-pyridyl)pyrazine. From ¹H NMR spectral data, the two deeb ligands are attached to Ir cis to each other. Mass spectra contain fragmentation patterns of the (M-PF₆)⁺ and (M-3PF₆)³⁺ molecular ions for [Ir(deeb)₂Cl₂](PF₆) and [Ir(deeb)₂(dpp)](PF₆)₃, respectively. The electronic absorption spectrum of [Ir(deeb)₂Cl₂](PF₆) shows maxima at 308 nm and 402 nm, which are assigned as ¹π → π* and metal-to-ligand charge transfer transitions, respectively. [Ir(deeb)₂(dpp)](PF₆)₃ exhibits peaks due to ¹π → π* transitions at 322 nm and 334 nm. [Ir(deeb)₂Cl₂](PF₆) has emission peaks at 538 nm in acetonitrile and 567 nm in the solid state, with lifetimes of 1.71 µs and 0.35 µs, respectively. [Ir(deeb)₂Cl₂](PF₆) has an unusually higher quantum yield than analogous compounds. [Ir(deeb)₂(dpp)](PF₆)₃ has emission peaks at 540 nm in acetonitrile and 599 nm in the solid state with lifetimes of 1.23 µs and 0.14 µs, respectively. Cyclic voltammetry of [Ir(deeb)₂Cl₂](PF₆) yields two reversible couples at −0.72 and −0.87 V versus Ag/AgCl, both corresponding to deeb ligand reductions, and a quasi-reversible couple at −1.48 V corresponding to Ir^3+/+ reduction. Electrochemical reduction of [Ir(deeb)₂(dpp)](PF₆)₃ yields couples at −0.38, −0.54, −0.71, and −1.33 V, assigned as deeb^0/−, deeb^0/−, dpp^0/−, and Ir^3+/+ reductions, respectively.

Keywords:

• deeb
• Bipyridine
• Photochemistry

Acknowledgments

We would like to thank Mr William Bebout of the Analytical Services Laboratory, Department of Chemistry at Virginia Tech for the mass spectral data and Mr Rongwei Zhou for his help in preparing the solid emission sample holders. We are also grateful to the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Sciences, US Department of Energy DE FG02-05ER15751 for partial support of this work.