Tris-cyclometalated Iridium Complexes Research Articles

Highly Efficient, Selective, and General Method for the Preparation of Meridional Homo- and Heteroleptic Tris-cyclometalated Iridium Complexes

A highly efficient and general method based on transmetalation with an organozinc reagent is developed for selective preparation of homo- and heteroleptic meridional tris-cyclometalated iridium complexes. The molecular structure of mer-Ir(1-piq)2(ppy) (2) has been determined by a single-crystal X-ray diffraction analysis. The emission properties of a series of meridional complexes are reported.

Photophysical and Electrochemical Properties of Heteroleptic Tris-Cyclometalated Iridium(III) Complexes

Mixed (difluoro)phenylpyridine/(difluoro)phenylpyrazole tris-cyclometalated iridium complexes were prepared in order to study the effect of fluorination and the pyridine/pyrazole ratio on the emission and electrochemical properties. Increasing fluorination and replacement of pyridine by pyrazole both leads to a widening of the HOMO-LUMO gap and generally leads to a blue shift in emission.

Synthesis and X-ray crystal structure of a heteroleptic tris-cyclometalated iridium(III) complex

A convenient synthesis of the tris-cyclometalated complex [Ir(ppy) 2(nppy)] ( 2, ppy = 2-phenylpyridyl, nppy = 2-(4-nitrophenyl)pyridyl) from [{Ir(μ-Cl)(ppy) 2} 2] ( 1), the ligand 2-(4-nitrophenyl)pyridine, and silver trifluoroacetate as halide abstractor in refluxing methoxyethanol is described. The crystal and molecular structure of 2 was determined by a single-crystal X-ray diffraction study.

Oligo(fluorenyl)pyridine ligands and their tris-cyclometalated iridium(iii) complexes: synthesis, photophysical properties and electrophosphorescent devices

The new extended tri- and penta-fluorenylpyridine ligands Fl3Py 2 and Fl5Py 3 and their tris-cyclometalated iridium(III) complexes Ir[Fl3Py]35 and Ir[Fl5Py]36 have been synthesised and their properties compared with the known iridium(III) complex Ir[Fl1Py]34. The lowest energy (emissive) excited states of the complexes 4–6 are dominated by ligand centred (LC) π→π* triplet states, as observed for their uncomplexed ligands 1–3. The emission maximum of complex 4 is ∼546 nm with a triplet lifetime of 2.8 µs. For complexes 5 and 6 the emission maxima are both ∼566 nm with triplet lifetimes of 7.4 µs and 7.8 µs, respectively. Devices made from poly(9,9′-spirobifluorene) (PSF) as the host and doped with complexes 4–6 show good stability; the EL spectra are unchanged after repeated operation over several days. Devices containing complexes 5 and 6 exhibit higher external quantum efficiency (EQE) values. Turn-on voltages of ∼3 V, giving an EQE of 2.8% at a current density of 30 mA cm−2, with a power efficiency of 4.3 lm W−1 and electroluminescence (EL) intensity of 25 000 cd m−2 at 550 mA cm−2 were observed for ITO/PEDOT ∶ PSS/PSF ∶ 6/Ca/Al devices.

Practical Syntheses ofN-Hexylcarbazol-2-yl- and -3-yl-boronic Acids, Their Cross-Coupled Products and a Derived Tris-cyclometalated (Pyridin-2-yl)carbazole Iridium(III) Complex

The syntheses of N-hexylcarbazol-2-yl- and -3-yl-boron- ic acids (1 and 2) are described on a ca. 7 g scale, starting from com- mercially available 2,5-dibromonitrobenzene (4) and carbazole (11), respectively. Compounds 1 and 2 underwent efficient palladi- um-catalyzed cross-coupling reactions under Suzuki-Miyaura con- ditions to yield products 17, 18 and 20. Compound 18 reacted with IrCl3 to give the tris-cyclometalated (pyridin-2-yl)carbazole iridi- um(III) complex 21, the X-ray crystal structure of which is reported.

Diastereoselective formation of chiral tris-cyclometalated iridium (III) complexes: characterization and photophysical properties.

Chiral, facial tris-cyclometalated Ir(III) complexes, fac-Delta-Ir(pppy)(3), fac-Lambda-Ir(pppy)(3), fac-Lambda-IrL (where pppy is (8R,10R)-2-(2'-phenyl)-4,5-pinenopyridine and L is a tripodal ligand comprising three pppy moieties connected through a mesityl spacer) have been synthesized and characterized. In IrL, NMR and CD studies indicate that only one diastereomer is formed, with the Lambda configuration at the metal center, whereas enantiopure pppy yields the fac-Lambda- and the fac-Delta-stereoisomer in a ratio 2:3. fac-Lambda-IrL was structurally characterized using X-ray crystallography. The luminescence properties including CPL, of the three complexes and their sensitivity to dioxygen were examined.

Synthesis and characterization of facial and meridional tris-cyclometalated iridium(III) complexes.

The synthesis, structures, electrochemistry, and photophysics of a series of facial (fac) and meridional (mer) tris-cyclometalated Ir(III) complexes are reported. The complexes have the general formula Ir(C'N)(3) [where C'N is a monoanionic cyclometalating ligand; 2-phenylpyridyl (ppy), 2-(p-tolyl)pyridyl (tpy), 2-(4,6-difluorophenyl)pyridyl (46dfppy), 1-phenylpyrazolyl (ppz), 1-(4,6-difluorophenyl)pyrazolyl (46dfppz), or 1-(4-trifluoromethylphenyl)pyrazolyl (tfmppz)]. Reaction of the dichloro-bridged dimers [(C'N(2)Ir(mu-Cl)(2)Ir(C'N)(2)] with 2 equiv of HC( wedge )N at 140-150 degrees C forms the corresponding meridional isomer, while higher reaction temperatures give predominantly the facial isomer. Both facial and meridional isomers can be obtained in good yield (>70%). The meridional isomer of Ir(tpy)(3) and facial and meridional isomers of Ir(ppz)(3) and Ir(tfmppz)(3) have been structurally characterized using X-ray crystallography. The facial isomers have near identical bond lengths (av Ir-C = 2.018 A, av Ir-N = 2.123 A) and angles. The three meridional isomers have the expected bond length alternations for the differing trans influences of phenyl and pyridyl/pyrazolyl ligands. Bonds that are trans to phenyl groups are longer (Ir-C av = 2.071 A, Ir-N av = 2.031 A) than when they are trans to heterocyclic groups. The Ir-C and Ir-N bonds with trans N and C, respectively, have bond lengths very similar to those observed for the corresponding facial isomers. DFT calculations of both the singlet (ground) and the triplet states of the compounds suggest that the HOMO levels are a mixture of Ir and ligand orbitals, while the LUMO is predominantly ligand-based. All of the complexes show reversible oxidation between 0.3 and 0.8 V, versus Fc/Fc(+). The meridional isomers are easier to oxidize by ca. 50-100 mV. The phenylpyridyl-based complexes have reduction potentials between -2.5 and -2.8 V, whereas the phenylpyrazolyl-based complexes exhibit no reduction up to the solvent limit of -3.0 V. All of the compounds have intense absorption bands in the UV region assigned into (1)(pi --> pi) transitions and weaker MLCT (metal-to-ligand charge transfer) transitions that extend to the visible region. The MLCT transitions of the pyrazolyl-based complexes are hypsochromically shifted relative to those of the pyridyl-based compounds. The phenylpyridyl-based Ir(III) tris-cyclometalates exhibit intense emission both at room temperature and at 77 K, whereas the phenylpyrazolyl-based derivatives emit strongly only at 77 K. The emission energies and lifetimes of the phenylpyridyl-based complexes (450-550 nm, 2-6 micros) and phenylpyrazolyl-based compounds (390-440 nm, 14-33 micros) are characteristic for a mixed ligand-centered/MLCT excited state. The meridional isomers for both pyridyl and pyrazolyl-based cyclometalates show markedly different spectroscopic properties than do the facial forms. Isolated samples of mer-Ir(C( wedge )N)(3) complexes can be thermally and photochemically converted to facial forms, indicating that the meridional isomers are kinetically favored products. The lower thermodynamic stabilities of the meridional isomers are likely related to structural features of these complexes; that is, the meridional configuration places strongly trans influencing phenyl groups opposite each other, whereas all three phenyl groups are opposite pyridyl or pyrazolyl groups in the facial complexes. The strong trans influence of the phenyl groups in the meridional isomers leads to the observation that they are easier to oxidize, exhibit broad, red-shifted emission, and have lower quantum efficiencies than their facial counterparts.