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 Ir3+/+ 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 deeb0/−, deeb0/−, dpp0/−, and Ir3+/+ reductions, respectively.