Iridium(III) Tris-cyclometalated Complexes with Diphenyloxazolic Ligands: Influence of Ligand Structure on Electrochemical and Photophysical Properties

The synthesis of cyclometalated platinum(II) complexes with benzoaryl-pyridines as C^N ligands for investigating their photophysical, electrochemical and electroluminescent properties

A series of (C^N)Pt(acac)-type complexes has been successfully synthesized with a benzo[b]furan, benzo[b]thiophene, benzo[b]selenophene, or benzo[b]tellurophene group in the benzoaryl-pyridine ligand. Using X-ray crystallography, the chemical structures of the complexes with benzo[b]selenophene and benzo[b]tellurophene groups have been clearly revealed. The photophysical, electrochemical, and electroluminescent (EL) behaviors of these (C^N)Pt(acac)-type complexes have been fully characterized. Furthermore, both time-dependent functional theory (TD-DFT) and natural transition orbital (NTO) theoretical results have been obtained to gain insight into the absorption and emission features. It has been shown that both the absorption bands with the lowest energy and the phosphorescence emission behaviors are dominated by the benzoaryl-pyridine cyclometalating ligand. Importantly, the effects of the group VIA atoms on the properties of these (C^N)Pt(acac)-type complexes have been revealed. Owing to the rareness of (C^N)Pt(acac)-type complexes with benzo[b]selenophene and benzo[b]tellurophene groups, their EL abilities have been characterized using solution-processed organic light-emitting diodes (OLEDs). The optimized red OLEDs with the complex bearing a benzo[b]selenophene unit show a maximum external quantum efficiency (ηext) of 6.3%, current efficiency (ηL) of 10.5 cd A-1, and power efficiency (ηP) of 9.1 lm W-1, while the EL device with the complex bearing a benzo[b]tellurophene unit can give deep-red emission at ca. 636 nm with ηext of 6.3%, ηL of 6.5 cd A-1, and ηP of 5.8 lm W-1. This research not only provides novel (C^N)Pt(acac)-type complexes, but also furnishes critical information regarding the photophysical and EL behavior of these new complexes.

Formylated chloro-bridged iridium(iii) dimers as OLED materials: opening up new possibilities

In this study, a series of four formyl-substituted chloro-bridged iridium(iii) dimers were prepared.

Glycerol as suitable solvent for the synthesis of metallic species and catalysis

This Minireview considers the foremost reported works involving glycerol as a solvent in the synthesis of organometallic complexes and metallic nanoparticles. This analysis highlights their catalytic applications. A special emphasis is devoted to the ability of glycerol to immobilize nanometric species, which, in turn, enables an efficient recycling of the catalytic phase to give metal-free organic products.

Tuning the photophysical properties of cationic iridium(III) complexes containing cyclometallated 1-(2,4-difluorophenyl)-1H-pyrazole through functionalized 2,2'-bipyridine ligands: blue but not blue enough

Four new heteroleptic iridium(III) complexes in the family [Ir(dfppz)(2)(N^N)](+), where Hdfppz = 1-(2,4-difluorophenyl)-1H-pyrazole and N^N = 6-phenyl-2,2'-bipyridine (1), 4,4'-(di-tert-butyl)-6-phenyl-2,2'-bipyridine (2), 4,4'-(di-tert-butyl)-6,6'-diphenyl-2,2'-bipyridine (3) and 4,4'-bis(dimethylamino)-2,2'-bipyridine (4), have been synthesized as the hexafluoridophosphate salts and fully characterized. Single crystal structures of ligand 3 and the precursor [Ir(2)(dfppz)(4)(μ-Cl)(2)] have been determined, along with the structures of the complexes 4{[Ir(dfppz)(2)(1)][PF(6)]}·3CH(2)Cl(2), [Ir(dfppz)(2)(3)][PF(6)]·CH(2)Cl(2) and [Ir(dfppz)(2)(4)][PF(6)]·CH(2)Cl(2). The role of inter- and intramolecular face-to-face π-stacking in the solid state is discussed. In the [Ir(dfppz)(2)(N^N)](+) (N^N = 1-3) cations, the phenyl substituent in ligands 1, 2 or 3 undergoes hindered rotation on the NMR timescale at 298 K in solution and the systems have been studied by variable temperature NMR spectroscopy. Acetonitrile solutions of [Ir(dfppz)(2)(N^N)][PF(6)] (N^N = 1-3) exhibit similar absorption spectra arising from ligand-based transitions; absorption intensity is enhanced on going to [Ir(dfppz)(2)(4)][PF(6)] and the spectrum extends further into the visible region. Acetonitrile solutions of the complexes are blue emitters with λ(em) = 517, 505, 501 and 493 nm for N^N = 1, 2, 3 and 4, respectively (λ(exc) = 280-310 nm). The redox behaviours of [Ir(dfppz)(2)(N^N)][PF(6)] (N^N = 1-3) are similar, and the introduction of the electron-donating NMe(2) substituents onto the N^N ligand shifts the metal-centred oxidation to less positive potentials. Theoretical calculations predict a mixed metal-to-ligand/ligand-to-ligand charge transfer (MLCT/LLCT) character for the emitting triplet state in agreement with the broad and unstructured character of the emission bands. The NMe(2) substituents enlarge the HOMO-LUMO gap and blue-shifts the emission of [Ir(dfppz)(2)(4)](+) that is centred on the ancillary ligand. These complexes, when processed into a thin film and sandwiched between two electrodes, lead to very low voltage operating electroluminescent devices. No additional components are needed, which demonstrates their electron and hole transport abilities in conjunction with the luminescent properties.

Control of the mutual arrangement of cyclometalated ligands in cationic iridium(III) complexes. Synthesis, spectroscopy, and electroluminescence of the different isomers

Synthetic control of the mutual arrangement of the cyclometalated ligands (C^N) in Ir(III) dimers, [Ir(C^N)(2)Cl](2), and cationic bis-cyclometalated Ir(III) complexes, [Ir(C^N)(2)(L^L)](+) (L^L = neutral ligand), is described for the first time. Using 1-benzyl-4-(2,4-difluorophenyl)-1H-1,2,3-triazole (HdfptrBz) as a cyclometalating ligand, two different Ir(III) dimers, [Ir(dfptrBz)(2)Cl](2), are synthesized depending on the reaction conditions. At 80 °C, the dimer with an unusual mutual cis-C,C and cis-N,N configuration of the C^N ligands is isolated. In contrast, at higher temperature (140 °C), the geometrical isomer with the common cis-C,C and trans-N,N arrangement of the C^N ligand is obtained. In both cases, an asymmetric bridge, formed by a chloro ligand and two adjacent nitrogens of the triazole ring of one of the cyclometalated ligands, is observed. The dimers are cleaved in coordinating solvents to give the solvento complexes [Ir(dfptrBz)(2)Cl(S)] (S = DMSO or acetonitrile), which maintain the C^N arrangement of the parent dimers. Controlling the C^N ligand arrangement in the dimers allows for the preparation of the first example of geometrical isomers of a cationic bis-cyclometalated Ir(III) complex. Thus, N,N-trans-[Ir(dfptrBz)(2)(dmbpy)](+) (dmbpy = 4,4'-dimethyl-2,2'-bipyridine), with cis-C,C and trans-N,N arrangement of the C^N ligands, as well as N,N-cis-[Ir(dfptrBz)(2)(dmbpy)](+), with cis-C,C and cis-N,N C^N ligand orientation, are synthesized and characterized. Interestingly, both isomers show significantly different photophysical and electroluminescent properties, depending on the mutual arrangement of the C^N ligands. Furthermore, quantum chemical calculations give insight into the observed photophysical experimental data.