Study on a set of bis-cyclometalated Ir(iii) complexes with a common ancillary ligand

Abstract

Bis-cyclometalated iridium(III) complexes [Ir(F2ppy)2ZN] (FZN), [Ir(F2CNppy)2ZN] (FCZN), [Ir(DMAF2ppy)2ZN] (FDZN) and [Ir(MeOF2ppy)2ZN] (MeOFZN) (F2ppy = 4',6'-difluoro-2-phenylpyridinate, F2CNppy = 5-cyano-4',6'-difluoro-2-phenylpyridinate, DMAF2ppy = 4',6'-difluoro-4-dimethylamino-2-phenylpyridinate, MeOF2ppy = 4',6'-difluoro-4-methyl-2-phenylpyridinate and ZN = 3,5-dimethylpyrazole-N-carboxamide) emitting in the sky blue region were synthesized. We studied the effect of the ancillary ligand ZN and the substituents on the cyclometalating ligands on the crystal structures, photophysical and electrochemical properties and the frontier orbitals. Density functional theory (DFT) calculation results indicate that in FCZN and FDZN the cyclometalating ligands show negligible participation in the HOMO, the ancillary ligand ZN being the main participant along with the Ir(III) d-orbitals. MeOFZN exhibits the maximum photoluminescence quantum efficiency and radiative emission rates along with the dominant low frequency metal-ligand vibrations and maximum reorganization energy in the excited state. All the substituted complexes show more polar characteristics than FZN, FCZN possessing the highest dipole moment among the complexes. The performances of the solution-synthesised organic light emitting devices (OLEDs) of FZN, FCZN and FDZN doped in a blend of mCP (m-bis(N-carbazolylbenzene)) and polystyrene are studied.

Transition-metal phosphors with cyclometalating ligands: fundamentals and applications

“…A typical procedure involves a prior preparation of the chloride-bridged dimers with formula [(C 4 N) 2 Ir(m-Cl)] 2 , followed by conversion to the anticipated heteroleptic complexes by replacing the chlorides with other easily accessible L 4 X ancillary chelates (L 4 X is a bidentate chelate constructed from a neutral L and an anionic X entity), such as acetylacetonate (acac), functionalized b-diketonate, N-methylsalicylimine (sal) or picolinate (pic). 10,45 Many of the heteroleptic complexes [Ir(C 4 N) 2 (L 4 X)] are known to exhibit room-temperature phosphorescence similar to those of the tris-cyclometalated complexes, leading to the conclusion that the luminescence is mainly controlled by the common [Ir(C 4 N) 2 ] fragment, while the emission wavelength is strongly dependent on the choice of C 4 N cyclometalating ligands; that is, a more extended electron delocalization would exhibit red-shifting of emission wavelengths. Such a generalized observation then provides a practical advantage, since the related homoleptic (i.e.…”

Heteroleptic Ir(iii) complexes containing both azolate chromophoric chelate and diphenylphosphinoaryl cyclometalates; Reactivities, electronic properties and applications

“…The filtrate was concentrated on a rotavap to give a crude product, which was then purified by silica gel column chromatography using a 1 : 1 mixture of ethyl acetate and hexane as eluent. Finally, the yellow crystals were crystallized from a mixture of CH 2 Cl 2 and hexane at RT (4,31 (d, J = 8.5 Hz, 1H), 6.79 (t, J = 9.0 Hz, 2H), 6.73 (t, J = 7.0 Hz, 1H), 6.66 (t, J = 8.0 Hz, 1H), 6.38 (td, J = 7.5, 2.5 Hz, 2H), 6.12 (d, J = 7.0 Hz, 1H), 5.87 (t, J = 10.0 Hz, 2H), 1.59 (s, 3H N,3.20;C,60.33;H,3.80. Found: N,2.94;C,60.48;H,4.11. Synthesis of [Ir(dpna) 2 (fppz)] (5a and 5b) from 2.…”

Effect of secondary ligands’ size on energy transfer and electroluminescent efficiencies for a series of europium(iii) complexes, a density functional theory study

“…This can lead to a local electric field, which can induce the charges, thus facilitating charge injection into the dopant. 36 This results in the hole and electron trapping balance in Eu-DDPz, and this may be another reason leading to the pure 612 nm emission. While for Eu-PyPhen and Eu-MPP, at higher relative applied voltage, holes can be firstly injected into the HOMO of dopants, and then electrons can be injected into the CBP layer, because it has been demonstrated that holes are the majority carrier in EML due to the lower energy barrier of hole injection into the EML than electron.…”