Cyclometalated Iridium(III) Complexes Incorporating Aromatic Phosphonate Ligands: Syntheses, Structures, and Tunable Optical Properties

Abstract

The incorporation of phosphonate ligands into the cyclometalated iridium(III) complexes can not only tune their electronic and optical properties but also provide the possibility of anchoring these molecules on the semiconductor surfaces for further applications. Herein, we report the first examples of mononuclear cyclometallated iridium(III) complexes incorporating phosphonate ligands, namely, [Ir(ppy)2(HL1)]·0.5H2O (1), [Ir(ppy)2(HL2)]·0.5H2O (2), [Ir(dfppy)2(HL1)] (3), and [Ir(dfppy)2(HL2)]·3.5H2O (4) (ppy = 2-phenylpyridine, dfppy = 2-(2,4-difluorophenyl)pyridine, H2L1 = 2-pyridylphosphonic acid, H2L2 = 2-quinolinephosphonic acid). Luminescent spectra are studied both in solution and in the solid state, and significantly red-shifted broad emission bands are observed in complexes 2 and 4. The experimental and density functional theory (DFT) time-dependent-DFT calculation results indicate that the expansion of the aromatic conjugation length in the ancillary phosphonate ligands decreases the lowest unoccupied molecular orbital energy levels of the systems, originating from the triplet state associated with the ancillary ligand such as 3MLCT, 3LC, and 3LLCT charge-transfer transitions.

Bis[3,5-difluoro-2-(pyridin-2-yl)phenyl](4,4′-dimethoxy-2,2′-bipyridine)iridium(III) hexafluoridophosphate

“…This is consistent with a substantial trans effect directed by the carbon atoms of dfppy. This feature is also present in related structures in the literature, including for example Ir-N bonds to the trans-effected nitrogen atoms of the hydrogen pyridin-2-yl-phosophonato ligand of bis [3,5-difluoro-2-(pyridin-2-yl)phenyl](hydrogen pyridin-2-yl-phosphonato)iridium(III) [Ir-N = 2.153 (4) A ˚; Zeng et al, 2019], and of the bipyridine ligands in the structures of (2,2 0 -bipyridine)bis [3,5-difluoro-2 data reports plexes [ranging from 2.120 (4) to 2.141 (4) A ˚; Li et al, 2017;Moriuchi et al, 2012]. This arrangement maximizes the number of C-Ir-N interligand trans-interactions compared to other potential isomers that would orient only one of the bipyOMe nitrogen atoms across from a strong trans-donor carbon atom, or that would have both strong trans-donor carbon atoms opposing one another (i.e.…”

Synthesis, physicochemical characterization and antiproliferative activity of phosphino Ru(ii) and Ir(iii) complexes

“…The determined oxidation potentials for the studied iridium( iii ) complexes, referring to the Ir( iii )/( iv ) redox process, are in agreement with the literature data for other organometallic Ir( iii ) compounds with various ligands. 17,57–60 The position of the cathodic peak was slightly shifted towards the negative potential, while the anodic peak was shifted a little towards positive potentials simultaneously with the scan rate increase. These observations suggest a diffusion controlled redox process.…”

Engineering Heteronuclear Arrays from IrIII‐Metalloligand and CoII Showing Coexistence of Slow Magnetization Relaxation and Photoluminescence

“…These absorptions are arising from LC, MLCT and LLCT transitions. [ 63‐64 ] Upon excitation of a powder of 1 at 375 nm, a strong emission band appears at 553 nm (Figures 4b, S13), corresponding to the 3 MLCT transition as consequence of the heavy‐atom effect. The emission is red‐shifted comparing to the related metalloligand Ir(ppy‐COOH) 3 ( λ em = 510 nm), [ 65 ] suggesting that the energy gap is reduced after replacing one ppy‐COOH by an electron‐donating ligand 2,2’‐bipyridine.…”