You-Xuan Zheng

Highly Efficient Green and Blue-Green Phosphorescent OLEDs Based on Iridium Complexes with the Tetraphenylimidodiphosphinate Ligand

Two novel bis-cyclometalated iridium complexes are successfully applied in organic light-emitting diodes (OLEDs). Because of their better carrier transport ability and shorter excited stated lifetimes, good electroluminescence performances of the complexes are observed.

Quenching of Er(III) luminescence by ligand C–H vibrations: Implications for the use of erbium complexes in telecommunications

The authors have quantified the quenching of the luminescence lifetime of Er3+ ions in organic complexes due to the presence of CH vibrational oscillators as a function of their distance from the ion. They have shown that any hydrogen atoms within a sphere of at least 20A from an erbium ion will cause sufficient quenching to prohibit its use in telecommunications applications.

Syntheses, photoluminescence, and electroluminescence of a series of iridium complexes with trifluoromethyl-substituted 2-phenylpyridine as the main ligands and tetraphenylimidodiphosphinate as the ancillary ligand.

Five bis-cyclometalated iridium complexes with tifluoromethyl-substituted 2-phenylpyridine (ppy) at different positions of its phenyl group as the main ligands and tetraphenylimidodiphosphinate (tpip) as the ancillary ligand, 2-6 (1 is a trifluoromethyl-free complex), were prepared, and their X-ray crystallography, photoluminescence, and electrochemistry were investigated. The number and positions of trifluoromethyl groups at the phenyl ring of ppy greatly affected the emission spectra of Ir(3+) complexes, and their corresponding emission peaks at 533, 502, 524, 480, and 542 nm were observed at room temperature, respectively. Constructed with complexes 2-6 as the emitters, respectively, the organic light-emitting diodes (OLEDs) with the structure of indium-tin oxide/1,1-bis[4-(di-p-tolylamino)phenyl]cyclohexane (30 nm)/Ir (x wt %):bis[3,5-bis(9H-carbazol-9-yl)phenyl]diphenylsilane (15 nm)/1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl (45 nm)/LiF (1 nm)/Al (100 nm) showed good performances. Particularly, device G4 based on 4-trifluoromethyl-substituted complex 4 with x = 8 wt % obtained a maximum luminance of over 39000 cd m(-2) and maximum luminance efficiency (η(L)) and power efficiency (η(p)) of 50.8 cd A(-1) and 29.0 lm W(-1), respectively. The results suggested that all of the complexes 2-6 would have potential applications in OLEDs.

Electroluminescence based on a β-diketonate ternary samarium complex

The triplet energy state of the HTH [HTH: 4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)hexane-1,3-dione] ligand was measured to be 20 400 cm−1, which indicated that Sm(HTH)3phen (phen: 1,10-phenanthroline) is a good complex to produce strong PL intensity and high fluorescence yield. Electroluminescent (EL) devices using the Sm(HTH)3phen complex as the emissive center were fabricated by vapor deposition and spin-coating methods. The relative intensity of the EL spectra changed compared to the photoluminescence (PL) spectrum, which suggested that the luminescence mechanisms of PL and EL have differences. A luminance of 9 cd m−2 and a higher brightness of 21 cd m−2 were obtained from the devices ITO/TPD (40 nm)/Sm(HTH)3phen (50 nm)/PBD (30 nm)/Al (200 nm) and ITO/PVK (40 nm)/PVK∶Sm(HTH)3phen (2.5 wt%, 50 nm)/PBD (30 nm)/Al (200 nm), respectively.

Highly efficient green phosphorescent OLEDs based on a novel iridium complex

A new iridium(III) complex Ir(tfmppy)2(tfmtpip) (1, tfmppy = 4-trifluoromethylphenyl-pyridine, tfmtpip = tetra(4-trifluoromethylphenyl)imidodiphosphinate) was synthesized and applied in organic light-emitting diodes (OLEDs). The devices with the structures of ITO/TAPC (1,1-bis[4-[N,N-di(p-tolyl)amino]phenyl]cyclohexane, 40 nm)/1 (x wt%): mCP (N,N′-dicarbazolyl- 3,5-benzene, 20 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, 40 nm)/LiF (1 nm)/Al (100 nm) exhibited a maximum power efficiency (ηp,max) of 113.23 lm W−1 and a maximum current efficiency (ηc,max) of 115.39 cd A−1 (0.01342 mA cm2) at the doping level of 5 wt%, which is among the best performances for Ir(III) complex based OLEDs in the green-light-emitting region. Compared with our former work, the excellent device efficiencies are due to the use of TmPyPB as the electron-transporting/hole-blocking layer which has a relatively higher electron mobility than that of TPBi (2,2′,2′′-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)) and the introduction of the –CF3 moiety to the Ir(III) complex, which can increase the electron mobility of the complex. The device performances proved that the complex has potential applications as an efficient green emitter in OLEDs.

Photostable and efficient red-emitters based on zeolite L crystals

Photostable and efficient red-emitting host–guest materials have been obtained employing a ship in a bottle procedure by loading 2-thenoyltrifluoroacetone (tta) or tta and 1,10-phenthroline (phen) from gas phase into the channels of Eu3+-ZL crystals that exhibit disc-shaped morphology followed by treatment with ammonia gas. The resulting Eu3+(tta)x-ZL and Eu3+(tta)x(phen)y-ZL host–guest materials were characterized with XRD, SEM, absorption and photoluminescence spectroscopy. Two key findings have been made in this work: (1) The emission intensity and the lifetime of Eu3+ ions of the host–guest materials can be significantly increased by treatment with ammonia gas, and (2) the encapsulated europium(III) complexes in ZL crystals show remarkably increased photostability.

Efficient OLEDs with low efficiency roll-off using iridium complexes possessing good electron mobility

Two bis-cyclometalated iridium complexes (Ir1 and Ir2) with trifluoromethyl substituted bipyridine (2′,6′-bis(trifluoromethyl)-2,3′-bipyridine (L1) and 2′,6′-bis(trifluoromethyl)-2,4′-bipyridine (L2)) as the main ligands and tetraphenylimidodiphosphinate as the ancillary ligand were prepared, and their X-ray crystallography, photoluminescence, electrochemistry properties were investigated. The Ir1 and Ir2 complexes show green emissions at about 500 and 502 nm with high quantum efficiencies of 0.63 and 0.93, respectively. Moreover, they also exhibit higher electron mobility than that of Alq3 (tris-(8-hydroxyquinoline)aluminium). The organic light emitting diodes (OLEDs) with the structure of ITO/TAPC (1,1-bis[4-(di-p-tolylamino)phenyl]cyclohexane, 40 nm)/mCP (1,3-bis(9H-carbazol-9-yl)benzene, 10 nm)/Ir complex (8 wt%): PPO21 (3-(diphenylphosphoryl)-9-(4-(diphenylphosphoryl)phenyl)-9H-carbazole, 25 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, 50 nm)/LiF (1 nm)/Al (100 nm) showed excellent performances, partly due to their high quantum efficiency and high electron mobility. For the devices G1 and G2, the maximum current efficiency (ηc) values are as high as 101.96/99.97 cd A−1 and the maximum external quantum efficiencies of 31.6% and 30.5% with low electroluminescence efficiency roll-off. The ηc data still remain over 90 cd A−1 even at the luminance of 10000 cd m−2, which proves that the complexes have potential applications as efficient green emitters in OLEDs.

An infinite photoluminescent coordination nanotube [CuSCN(L)]·(DMF)0.5

A novel, single-walled coordination nanotube [CuSCN(L)]·(DMF)0.5 (L = 1,3-di(pyridin-4-yl)propane, DMF = N,N-dimethylformamide) was easily prepared using two bidentate ligands and characterized by single crystal X-ray diffraction, which shows guest exchange properties and strong photoluminescence at room temperature.

Syntheses, structures, photoluminescence, and magnetic properties of nanoporous 3D lanthanide coordination polymers with 4,4′-biphenyldicarboxylate ligand

Six three-dimensional nanoporous lanthanide coordination polymers, [Ln2(bpdc)3(HCOOH)2]n [Ln = Eu (1), Sm (2), La (3), Ce (4), Gd (5) and Nd (6)], were prepared by the solvothermal reactions of the LnIII ions with 4,4′-biphenyldicarboxylate (H2bpdc) in DMF solution. Crystallographic data show that compounds 1–6 are isomorphous and crystallize in monoclinic, space groupC2. Each LnIII is eight-coordinated to seven O atoms from six bpdc2− ligands and one O atom from HCOOH molecule in distorted bisdisphenoid coordination geometry. The adjacent LnIII ions are intraconnected by the carboxylate groups of the bpdc2− ligands to form a 1D inorganic rod-shaped chain [Ln(CO2)3]n. The inorganic chains are interconnected by the biphenyl groups, giving rise to a 3D framework that consists in two types of 1D open channels, with 15.11 × 27.05 A rhombic channels along the b axis and 8.66 × 15.91 A quadrate channels along the c axis without interpenetration. Compounds 1 and 6 are strong luminescent materials which exhibit characteristic EuIII emission bands in the visible region for 1 and NdIII emission bands in the near IR region for 6 upon excitation at 360 nm. The absence of the ligand emission can be ascribed to the energy transfer from the bpdc2− ligand to the LnIII ion during photoluminescence. The magnetic properties of compounds 1, 4, 5 and 6 have been investigated through the measurement of their magnetic susceptibilities over the temperature range of 1.8–300 K.

Circularly polarised phosphorescent photoluminescence and electroluminescence of iridium complexes.

Nearly all the neutral iridium complexes widely used as dopants in PhOLEDs are racemic mixtures; however, this study observed that these complexes can be separated into stable optically active Λ and ∆ isomers and that their chirality is an intrinsic property. The circularly polarised phosphorescent photoluminescence (CPPPL) signals of Λ/Δ isomers are perfect mirror images with opposite polarisation and equal intensity exhibiting a “handedness” for the polarisation. For the first time, we applied the Λ/Δ iridium isomers as emitters in OLEDs, and the circularly polarised phosphorescent electroluminescence (CPPEL) spectra reveal completely positive or negative broad peaks consistent with the CPPPL spectra. The results demonstrate that the Λ/Δ isomers have potential application for 3D OLEDs because they can exhibit high efficiency and luminance, and 3D display technology based on circularly polarised light is the most comfortable for the eyes.