Homoleptic tris(pyridyl pyrazolate) Ir(III) complexes: en route to highly efficient phosphorescent OLEDs.

Treatment of the metal reagent IrCl(3)nH(2)O with two equivalents of 2-pyridyl pyrazole (N;N)H (3-tert-butyl-5-(2-pyridyl) pyrazole, (bppz)H and 3-trifluoromethyl-5-(2-pyridyl) pyrazole, (fppz)H), afforded the isomeric Ir(III) metal complexes with a general formula cis-[Ir(bppz)(2)Cl(2)]H (2 a), trans-[Ir(bppz)(2)Cl(2)]H (3 a), cis-[Ir(fppz)(2)Cl(2)]H (2 b), and trans-[Ir(fppz)(2)Cl(2)]H (3 b). Single-crystal X-ray diffraction studies on 2 b and 3 a revealed the coexistence of two pyrazolate chelates and two terminal chloride ligands on the coordination sphere. Subsequent reactivity studies confirmed their intermediacy to the preparation of homoleptic mer-[Ir(bppz)(3)] (1 a) and mer-[Ir(fppz)(3)] (1 b) that showed dual intraligand and ligand-to-ligand charge-transfer phosphorescence at room temperature. To attain bright, room-temperature phosphorescence further, we then synthesized two isoquinolinyl pyrazolate complexes, mer-[Ir(bipz)(3)] (4 a) and mer-[Ir(fipz)(3)] (4 b) ((bipz)H=3-tert-butyl-5-(1-isoquinolyl) pyrazole and (fipz)H=3-trifluoromethyl-5-(1-isoquinolyl) pyrazole). Their orange luminescence is mainly attributed to the mixed MLCT/pipi* transition, and the quantum yields were as high as 86 (4 a) and 50 % (4 b) in degassed CH(2)Cl(2) solution at RT. The organic light-emitting diodes (OLEDs) were then fabricated by using 4 a as a dopant, giving orange luminescence with CIE(x,y)=0.55, 0.45 (CIE(x,y)=the 1931 Commission Internationale de L'Eclairage (x,y) coordinates) and peak efficiencies of 14.6 % photon/electron, 34.8 cd A(-1), 26.1 lm W(-1). The device data were then compared with the previously reported heteroleptic complex [Ir(dfpz)(2)(bipz)] (5) ((dfpz)H=1-(2,4-difluorophenyl) pyrazole), revealing the possible effect of the bipz chelate and phosphor design on the overall electrophosphorescent performance, which can be understood by the differences in the carrier-transport properties.

Neutral Ru(II)-based emitting materials: a prototypical study on factors governing radiationless transition in phosphorescent metal complexes.

In addition to the metal-centered dd transition that is widely accepted as a dominant radiationless decay channel, other factors may also play important roles in governing the loss of phosphorescence efficiency for heavy-transition-metal complexes. To conduct our investigation, we synthesized two dicarbonylruthenium complexes with formulas [Ru(CO)2(BQ)2] (1) and [Ru(CO)2(DBQ)2] (2), for which the cyclometalated ligands BQ and DBQ denote benzo[h]quinoline and dibenzo[f,h]quinoxaline, respectively. Replacing one CO ligand with a P donor ligand such as PPh2Me and PPhMe2 caused one cyclometalated ligand to undergo a 180 degrees rotation around the central metal atom, giving highly luminous metal complexes [Ru(CO)L(BQ)2] and [Ru(CO)L(DBQ)2], where L = PPh2Me and PPhMe2 (3-6), with emission peaks lambda(max) in the range of 571-656 nm measured in the fluid state at room temperature. It is notable that the S0-T1 energy gap for both 1 and 2 is much higher than that of 3-6, but the corresponding phosphorescent spectral intensity is much weaker. Using these cyclometalated Ru metal complexes as a prototype, our experimental results and theoretical analysis draw attention to the fact that, for complexes 1 and 2, the weaker spin-orbit coupling present within these molecules reduces the T1-S0 interaction, from which the thermally activated radiationless deactivation may take place. This, in combination with the much smaller 3MLCT contribution than that observed in 3-6, rationalizes the lack of room-temperature emission for complexes 1 and 2.

Iridium(III) complexes with orthometalated quinoxaline ligands: subtle tuning of emission to the saturated red color.

Rational design and syntheses of four iridium complexes (1-4) bearing two substituted quinoxalines and an additional 5-(2-pyridyl) pyrazolate or triazolate as the third coordinating ligand are reported. Single-crystal X-ray diffraction studies of 1 reveal a distorted octahedral geometry, in which two dpqx ligands adopt an eclipse configuration, for which the quinoxaline N atoms and the C atoms of orthometalated phenyl groups are located at the mutual trans- and cis-positions, respectively. The lowest absorption band for all complexes consists of a mixture of heavy-atom Ir(III)-enhanced 3MLCT and 3pipi* transitions, and the phosphorescent peak wavelength can be fine-tuned to cover the spectral range of 622-649 nm with high quantum efficiencies. The cyclic voltammetry was measured, showing a reversible, metal-centered oxidation with potentials at 0.76-1.03 V, as well as two reversible reduction waves with potentials ranging from -1.61 to -2.06 V, attributed to the sequential addition of two electrons to the more electron-accepting heterocyclic portion of two distinctive cyclometalated C/N ligands. Complex 1 was used as the representative example to fabricate the red-emitting PLEDs by blending it into a PVK-PBD polymer mixture. The devices exhibited the characteristic emission profile of 1 with peak maxima located at 640 nm. The maximum external quantum efficiency was 3.15% ph/el with a brightness of 1751 cd/m2 at a current density of 67.4 mA/cm2, and the maximum brightness of 7750 cd/m2 was achieved at the applied voltage of 21 V and with CIE coordinates of (0.64, 0.31).

A remarkable ligand orientational effect in osmium-atom-induced blue phosphorescence.

A new series of Os(II)-based carbonyl complexes cis(CO),trans(Npy,Npy),cis(Ntz,Ntz)-[Os(CO)2(bptz)2] (1), cis(CO),cis(Npy,Npy),trans(Ntz,Ntz)-[Os(bptz)2(CO)2] (2), and cis(CO),trans(Npy,Npy),cis(Ntz,Ntz)-[Os(CO)2(fptz)2] (3), where bptz and fptz denote 3-tert-butyl-5-(2-pyridyl)- and 3-trifluoromethyl-5-(2-pyridyl)-1,2,4-triazolate, respectively, have been designed and synthesized in an effort to achieve high efficiency, room-temperature blue phosphorescence. Although 1 and 2 are geometric isomers, remarkably different excited-state relaxation pathways were observed. Complex 1 exhibits strong phosphorescence in CH3CN (Phi(p) approximately 0.47) and as a single crystal at room temperature, whereas complex 2 is nearly nonemissive under similar conditions. The associated relaxation dynamics have been comprehensively investigated by spectroscopic and relaxation dynamics as well as by theoretical approaches. Our results lead us to the conclusion that for complex 2, the "loose bolt" effect of metal-ligand bonding interactions plays a crucial role in the fast radiationless deactivation of this type of geometrical isomer. Fine adjustment can also be achieved by functionalizing the ligands so that the electron-withdrawing nature of the CF3 group in 3 stabilizes the HOMO of the triazolate moiety, thus moving the emission further into the pure "blue" region; this results in highly efficient phosphorescence and renders 3 particularly attractive for application in blue OLED devices.

Fluorinated aminoalkoxide and ketoiminate indium complexes as MOCVD precursors for In2O3 thin film deposition.

The syntheses of two distinctive types of indium complex derived from trimethylindium (InMe(3)) are reported. The first kind has a generalized structural formula [InMe(2)(amak)](2), where (amak)H is an abbreviation for a series of chelating amino alcohol ligands HOC(CF(3))(2)CH(2)NHR, R = (CH(2))(2)OMe (1), Me (2), and Bu(t) (3), as well as HOC(CF(3))(2)CH(2)NMe(2) (4); while the second type of complex is illustrated by [InMe(2)(keim)] (5), for which (keim)H is a tridentate ketoimine ligand of structural formula O=C(CF(3))CH(2)C(CF(3))=NCH(2)CH(2)NMe(2). The solid-state structures of 2 and 5 were determined using single crystal X-ray diffraction studies. For the aminoalkoxide complexes 2-4, the existence of dimeric In(2)O(2) core structures in the solid state has been established with the amino fragment located trans to the alkoxide ligands, in a molecular arrangement which is in contrast to the distorted, trigonal bipyramidal geometry observed for the ketoiminate complex 5. Moreover, VT NMR studies of 2 revealed a rapid dimer-to-monomer equilibration and simultaneous rupture of the N-->In dative interaction, affording two interconvertible isomers related by having the N-Me substituents in either trans or cis dispositions. For complexes 2 and 5, deposition of In(2)O(3) thin films was successfully conducted at temperatures 400-500 degrees C, using O(2) as the carrier gas to induce indium oxide deposition and to suppress carbon impurity present in the thin film. Scanning electron micrographs (SEMs) revealed the surface morphologies. The atomic composition of these films was examined by both X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering (RBS) methods, while X-ray diffraction studies (XRD) confirmed the formation of a preferred orientation along the (222) planes.

Realizing green phosphorescent light-emitting materials from rhenium(i) pyrazolato diimine complexes.

Two neutral pyrazolato diimine rhenium(I) carbonyl complexes with formula [Re(CO)(3)(N-N)(btpz)] where N-N = 2,2'-bipyridine (1) and 1,10-phenanathroline (2), and btpz = 3,5-bis(trifluoromethyl) pyrazolate, were synthesized and characterized by elemental analysis, routine spectroscopic methods, and single-crystal X-ray diffraction study. Ground and excited state properties of these complexes were investigated by steady-state and time-resolved spectroscopies. Complexes 1 and 2 show photoluminescent emission in both solution and solid-state at room temperature, arising from metal to ligand charge-transfer (MLCT) transition with strong overlapping of intraligand pi --> pi transitions. The long-lived excited state lifetimes of complexes 1 and 2, which are on the order of microseconds, indicate the presence of phosphorescent emission. As these complexes hold the potential to serve as phosphors for organic light-emitting diodes (OLEDs), their electroluminescent performances were evaluated by employing them as dopants of various electron transport layer (ETL) or hole transport layer (HTL) hosts. For complex 1, a green electrophosphorescence emission centered at lambda(max) = 530 nm was observed at low turn-on voltage ( approximately 6 V) with luminous power efficiency of 0.72 lm/W, external quantum efficiency of 0.82%, and luminance of 2300 cd/m(2) at a current density of 100 mA/cm(2).