Abstract:

A series of luminescent cyclometalated Ir(III) complexes functionalized with amide derivatives were prepared and compared with [Ir(ppy)₂phen-NH₂]Cl. The complexes were [Ir(ppy)₂phen-Br]Cl, [Ir(ppy)₂phen-COOH]Cl, and [Ir(ppy)₂phen-Si]Cl, where ppy is 2-phenylpyridine, phen-NH₂ is 5-amino-^{[1, 10]}-phenanthroline, phen-Br is 2-bromo-2-methyl-N-(1, 10-phenanthrolin-5-yl)propanamide, phen-COOH is 4-[(1, 10-phenanthrolin-5-yl)amino]-4-oxobut-2-enoic acid, and phen-Si is 5-[N, N-bis-3-(triethoxysilyl) propyl]ureyl-1, 10-phenanthroline. They were characterized using nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry (MS), ultraviolet-visible (UV-Vis) absorption spectroscopy, photoluminescence (PL) spectroscopy, and cyclic voltammetry (CV). The three novel complexes have intense absorptions in the blue-purple region. The complexes show bright yellow to orange PL emissions under UV irradiation, and the quantum yields (Φ) of these complexes are higher than 12%. The excited-state lifetimes of the novel complexes are 9.18-12.00 μs, much longer than that of [Ir(ppy)₂phen-NH₂]Cl (5.78 μs). With both the highest quantum yield (32%) and longest lifetime (12.00 μs), [Ir(ppy)₂phen-Br]Cl also shows the best oxygen-sensing properties and the largest I₀/I factor, 10.91 (I₀: the PL intensity of the complex in the absence of O₂, I: the PL intensity of the complex under pure oxygen). These results suggest that [Ir(ppy)₂phen-Br]Cl may be a promising candidate for use in oxygen sensors based on covalent grafting. Time-dependent density functional theory (TD-DFT) calculations were used to supplement the photoelectric property studies. Theoretical calculations indicate that all the mononuclear complexes have approximately octahedral structures with Ir(III) as the coordination center. The computational results agree well with the experimental data.

Key words: Photoelectric property, Ir(III) complex, Phenanthroline, Oxygen quenching, Luminescence sensor