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 me...

The synthesis and photophysical characterization of a series of (N,C 2′ -(2-para-tolylpyridyl)) 2 Ir(LL′) [(tpy) 2 Ir(LL′)] (LL′ ) 2,4-pentanedionato (acac), bis(pyrazolyl)borate ligands and their analogues, diphosphine chelates and tertbutylisocyanide (CN-t-Bu)) are reported. A smaller series of [(dfppy) 2 Ir(LL′)] (dfppy ) N,C 2′ -2-(4′,6′-difluorophenyl)pyridyl) complexes were also examined along with two previously reported compounds, (ppy) 2 Ir(CN) 2and (ppy) 2 Ir(NCS) 2 -(ppy ) N,C 2′ -2-phenylpyridyl). The (tpy) 2 Ir(PPh 2 CH 2 ) 2 BPh 2 and [(tpy) 2 Ir(CN-t-Bu) 2 ](CF 3 SO 3 ) complexes have been structurally characterized by X-ray crystallography. The Ir−C aryl bond lengths in (tpy) 2 Ir(CN-t-Bu) 2 + (2.047-(5) and 2.072(5) Å) and (tpy) 2 Ir(PPh 2 CH 2 ) 2 BPh 2 (2.047(9) and 2.057(9) Å) are longer than their counterparts in (tpy) 2 Ir(acac) (1.982(6) and 1.985(7) Å). Density functional theory calculations carried out on (ppy) 2 Ir(CN-Me) 2 + show that the highest occupied molecular orbital (HOMO) consists of a mixture of phenyl-π and Ir-d orbitals, while the lowest unoccupied molecular orbital is localized primarily on the pyridyl-π orbitals. Electrochemical analysis of the (tpy) 2 Ir(LL′) complexes shows that the reduction potentials are largely unaffected by variation in the ancillary ligand, whereas the oxidation potentials vary over a much wider range (as much as 400 mV between two different LL′ ligands). Spectroscopic analysis of the cyclometalated Ir complexes reveals that the lowest energy excited state (T 1 ) is a triplet ligand-centered state ( 3 LC) on the cyclometalating ligand admixed with 1 MLCT (MLCT ) metal-to-ligand charge-transfer) character. The different ancillary ligands alter the 1 MLCT state energy mainly by changing the HOMO energy. Destabilization of the 1 MLCT state results in less 1 MLCT character mixed into the T 1 state, which in turn leads to an increase in the emission energy. The increase in emission energy leads to a linear decrease in ln(k nr ) (k nr ) nonradiative decay rate). Decreased 1 MLCT character in the T 1 state also increases the Huang−Rhys factors in the emission spectra, decreases the extinction coefficient of the T 1 transition, and consequently decreases the radiative decay rates (k r ). Overall, the luminescence quantum yields decline with increasing emission energies. A linear dependence of the radiative decay rate (k r ) or extinction coefficient ( ) on (1/∆E) 2 has been demonstrated, where ∆E is the energy difference between the 1 MLCT and 3 LC transitions. A value of 200 cm -1 for the spin−orbital coupling matrix element 〈 3 LC|H SO | 1 MLCT〉 of the (tpy) 2 Ir(LL′) complexes can be deduced from this linear relationship. The (fppy) 2 Ir(LL′) complexes with corresponding ancillary ligands display similar trends in excited-state properties.

Efficient blue‐, green‐, and red‐light‐emitting organic diodes are fabricated using binuclear platinum complexes as phosphorescent dopants. The series of complexes used here have pyrazolate bridging ligands and the general formula C∧NPt(μ‐pz)2PtC∧N (where C∧N = 2‐(4′,6′‐difluorophenyl)pyridinato‐N,C2′, pz = pyrazole (1), 3‐methyl‐5‐tert‐butylpyrazole (2), and 3,5‐bis(tert‐butyl)pyrazole (3)). The Pt–Pt distance in the complexes, which decreases in the order 1 > 2 > 3, solely determines the electroluminescence color of the organic light‐emitting diodes (OLEDs). Blue OLEDs fabricated using 8 % 1 doped into a 3,5‐bis(N‐carbazolyl)benzene (mCP) host have a quantum efficiency of 4.3 % at 120 Cd m–2, a brightness of 3900 Cd m–2 at 12 V, and Commission Internationale de L'Eclairage (CIE) coordinates of (0.11, 0.24). Green and red OLEDs fabricated with 2 and 3, respectively, also give high quantum efficiencies (∼ 6.7 %), with CIE coordinates of (0.31, 0.63) and (0.59, 0.46), respectively. The current‐density–voltage characteristics of devices made using dopants 2 and 3 indicate that hole trapping is enhanced by short Pt–Pt distances (< 3.1 Å). Blue electrophosphorescence is achieved by taking advantage of the binuclear molecular geometry in order to suppress dopant intermolecular interactions. No evidence of low‐energy emission from aggregate states is observed in OLEDs made with 50 % 1 doped into mCP. OLEDs made using 100 % 1 as an emissive layer display red luminescence, which is believed to originate from distorted complexes with compressed Pt–Pt separations located in defect sites within the neat film. White OLEDs are fabricated using 1 and 3 in three different device architectures, either with one or two dopants in dual emissive layers or both dopants in a single emissive layer. All the white OLEDs have high quantum efficiency (∼ 5 %) and brightness (∼ 600 Cd m–2 at 10 V).

No abstract

Complexation of the ligand 3-diphenylamino-4-hydroxycyclobut-3-ene-1,2-dione (diphenylaminosquarate) with metal salts of La, Eu, Gd and Tb produced the first set of lanthanide complexes with a monosubstituted aminosquarate ligand. The lanthanum complex La[(C6H5)2NC4O3]3(H2O)6·5H2O (1) is monomeric and crystallizes in the triclinic space group P1̄, with a nine-coordinate La center bonded to three pendant diphenylaminosquarate groups and six aqua ligands. The Eu, Gd, and Tb complexes [M(μ-(C6H5)2NC4O3)((C6H5)2NC4O3)(NO3)(OH2)4]2·4H2O (2−4) are isomorphous (also P1̄), each metal atom being nine-coordinate and bridged to its neighbor by two diphenylaminosquarate ligands in a μ-1,2- fashion; the coordination polyhedron around each metal is completed by a pendant diphenylaminosquarate ligand, four aqua ligands, and a chelating nitrate ion. The resistance of the diphenylamino substituent to hydrolysis, vis-à-vis the hydrolysis of dialkylamino substituents, is discussed.

The use of metal complexes fac-tris(1-phenylpyrazolato-N,C(2)('))cobalt(III) [fac-Co(ppz)(3)], fac-tris(2-phenylpyridinato-N,C(2)(') cobalt(III) [fac-Co(ppy)(3)], and [tris[2-((pyrrole-2-ylmethylidene)amino)ethyl]amine]gallium(III) [Ga(pma)] as materials for hole-transporting layers (HTL) in organic light-emitting diodes (OLEDs) is reported. Co(ppz)(3) and Co(ppy)(3) were prepared by following literature procedures and isolated as mixtures of facial (fac) and meridional (mer) isomers. The more stable fac isomers were separated from the unstable mer forms via column chromatography and thermal gradient sublimation. Crystals of fac-Co(ppz)(3) are monoclinic, space group P2(1)/c, with a = 13.6121(12) A, b = 15.5600(12) A, c = 22.9603(17) A, beta = 100.5 degrees, V = 4781.3(7) A(3), and Z = 8. [Tris[2-((pyrrol-2-ylmethylidene)amino)ethyl]amine]gallium [Ga(pma)] was prepared by the reaction of gallium(III) nitrate with the pmaH(3) ligand precursor in methanol. Ga(pma) crystallizes in the cubic space group I3d with cell parameters a = 20.2377(4) A, b = 20.2377(4) A, c = 20.2377(4) A, beta = 90.0 degrees, V = 8288.6(3) A(3), and Z = 16. These cobalt and gallium complexes are pale colored to colorless solids, with optical energy gaps ranging 2.6-3.36 eV. A two-layer HTL/ETL (ETL = electron-transporting layer) device structure using fac-Co(ppz)(3) and fac-Co(ppy)(3) as the HTL does not give efficient electroluminescence. However, the introduction of a thin layer of a hole-transporting material (N,N'-bis(1-naphthyl)-N,N'-diphenylbenzidine, NPD) as an energy "stair-step" and electron/exciton-blocker dramatically improves the device performance. Both fac-Co(ppz)(3) and fac-Co(ppy)(3) devices give external quantum efficiencies higher than 1.0%, with brightness 5000 and 7000 Cd/m(2) at 10 V, respectively. Ga(pma) also functions as an efficient interface layer, giving device performances very similar to those of analogous devices using NPD as the interface layer. Stability tests have been carried out for Co(ppz)(3)/NPD/Alq(3) and Co(ppy)(3)/NPD/Alq(3) devices. While fac-Co(ppy)(3) gave stable OLEDs, the fac-Co(ppz)(3)-based devices had very short lifetimes. On the basis of the experimental results of chemical oxidation of fac-Co(ppz)(3), the major cause for the fast decay of the fac-Co(ppz)(3) device is proposed to be the decomposition of fac-Co(ppz)(3)(+) in the HTL layer during the device operation.

Reaction of EuCl(3).6H(2)O with 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione (phenylsquarate) in methanol produces the polymeric complex {Eu(&mgr;-C(6)H(5)C(4)O(3))(2)(C(6)H(5)C(4)O(3))(2)(CH(3)OH)(2)(H(2)O)(2).(CH(3)OH)}(n)() (1) which crystallizes in the space group P2(1)/n with a = 13.4049(5) Å, b = 13.7043(7) Å, c = 18.5026(6) Å, beta = 106.351(4) degrees, and Z = 4. The Eu(III) ion is eight coordinate with two bridging and two pendant phenylsquarate ligands, the coordination polyhedron being completed by two aqua and two methanol ligands. The emission spectra of 1 and the already reported europium(III) squarate, [Eu(H(2)O)(4)](2)(C(4)O(4))(3) (2), and europium(III) (diphenylamino)squarate, {Eu[&mgr;-(C(6)H(5))(2)NC(4)O(3)](2)[(C(6)H(5))(2)NC(4)O(3)][NO(3)][H(2)O](4)}(2).4H(2)O (3) show emissions dominated by the Eu(3+)((5)D(0) --> (7)F(j)) transitions which are typical for Eu(3+) species in low-symmetry sites. For 1 the emission occurs at room temperature and is apparently sensitized by the phenyl substituents on the phenylsquarate ligand groups; for 2 and 3 the emission is only observed at low temperature (77 K). The broad band (370-575 nm) in the excitation spectrum of 3 at 77 K is consistent with excimer formation, which can be attributed to enhanced pi-pi interactions between the C(4)-cycles of neighboring phenylsquarate ligand groups whose centroid.centroid separation decreases from 3.630(7) Å at room temperature (293 K) to 3.565(7) Å at 96 K. The temperature dependence of the luminescence of all three complexes revealed strong Eu.Eu interactions which keep the energy transport process in the dynamic regime.

The synthesis and characterization by single-crystal X-ray crystallography of a series of monomeric first-row transition-metal complexes with the 1-methoxycyclobutenedionate(1-) ligand are described. The isomorphous compounds [M(CH(3)OC(4)O(3))(2)(H(2)O)(4)] (M = Mn, Co, Ni, Zn) are C(2) symmetric and crystallize in the monoclinic space group C2/c. The metal atom in each of these complexes is six-coordinate with two cis 1-methoxycyclobutenedionate(1-) ligands, the methoxy substituent being oriented cis with respect to the ligating oxygen atom. The remaining coordination sites are filled by four aqua ligands. Monomers are linked by O-H.O hydrogen bonds to form arrays of stepped tapes. Hydrolysis of the methoxy group on the ligand occurs during the formation of the copper complex and {[Cu(C(4)O(4))(H(2)O)(2)].0.25H(2)O}(n)() is produced. This complex crystallizes in the tetragonal space group P4/n and has a structure similar to, but differing significantly from, those of a series of 3-dimensional cage squarates which have been reported previously.