Synthesis, photophysical and TD-DFT evaluation of triphenylphosphonium-labeled Ru(II) and Ir(III) luminophores

Abstract

The chemistry of 5-acetamido derivatized 1,10-phenanthroline was developed to yield a series of pro-ligands (L^1–4) and related triphenylphosphonium (TPP+) appended cationic variants (L^5–8). The resulting heteroleptic complexes [Ru(bipy)2(L^1–8)]n+ (where bipy = 2,2′-bipyridine) and cyclometalated species [Ir(tmq)2(L^1–8)]n+ (where tmq = 2,6,7-trimethyl-3-phenylquinoxaline) were isolated and fully characterized using a range of analytical and spectroscopic methods, including electrochemistry and time-resolved photophysics. Multinuclear NMR spectroscopies were used to characterize the compounds, including ³¹P NMR showing δP 21.3–24.4 ppm for the phosphonium species. Two X-ray crystal structures were successfully obtained on TPP⁺ functionalized Ru(II) and Ir(III) species: key features include the distorted octahedral coordination spheres, and the defined spatial relationships between the complex core and the TPP+ unit. All Ru(II) and Ir(III) complexes were phosphorescent in the red region with ³MLCT or ³MLCT/³LLCT character, respectively. Comparison across the series suggest the presence of the TPP+ unit induced moderate quenching of the complex phosphorescence. A comparison with quaternary ammonium analogues suggests this may be due to differences in ion pairing and solvation phenomena in the TPP+ complexes.

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Identifiers

ORCID for Peter N. Horton: orcid.org/0000-0001-8886-2016

ORCID for Simon J. Coles: orcid.org/0000-0001-8414-9272

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