Guan-Ru Lee

Highly bright blue organic light-emitting devices using spirobifluorene-cored conjugated compounds

An efficient and morphologically stable pyrimidine-containing spirobifluorene-cored oligoaryl, 2,7-bis[2-(4-tert-butylphenyl)pyrimidine-5-yl]-9,9′-spirobifluorene (TBPSF), as an emitter or a host for blue organic light-emitting devices (OLEDs), is reported. The steric hindrance inherent with the molecular structure renders the material a record-high neat-film photoluminescence (PL) quantum yield of 80% as a pure blue emitter (PL peak at 430 nm) of low molecular weight, and a very high glass-transition temperature (Tg) of 195 °C. Blue OLEDs employing this compound as the emitter or the emitting host exhibit unusual endurance for high currents over 5000 mA/cm2. When TBPSF is used as a host for perylene in a blue OLED, maximal brightness of ∼80 000 cd/m2 had been achieved, representing the highest values reported for blue OLEDs under dc driving.

Energy structures and chemical reactions at the Al∕LiF∕Alq3 interfaces studied by synchrotron-radiation photoemission spectroscopy

The chemical properties and energy levels of Al∕LiF∕Alq3 were investigated via high-resolution synchrotron-radiation photoemission spectroscopy. No clear chemical reaction was found with LiF deposited on Alq3. The core-level spectra show that Li+ ion and Alq3 anion are created only after Al is deposited on LiF∕Alq3 surfaces. Combined with the increase of the electron concentrations indicated by the Fermi-level position in valence-band spectra, the results provide direct evidence of the proposed chemical reaction, 3LiF+Al+3Alq3→AlF3+3Li+Alq3−, which leads to the excellent electron injection efficiency in Al∕LiF∕Alq3.

Electronic and chemical properties of molybdenum oxide doped hole injection layers in organic light emitting diodes

The origins of barrier lowering leading to high efficient organic light emitting devices with incorporation of molybdenum oxide (MoOx) in anode structures are investigated. Ultraviolet and x-ray photoemission spectra reveal that p-type doping effects in the organic films and carrier concentration increase at the anode interfaces cause the hole injection barrier lowering. The gap states, which help carrier injection from the anodes, resulted from the oxygen deficiency in MoOx due to the interaction of organic materials and MoOx.

Electronic and chemical properties of cathode structures using 4,7-diphenyl-1,10-phenanthroline doped with rubidium carbonate as electron injection layers

The electronic properties and chemical interactions of cathode structures using 4,7-diphenyl-1, 10-phenanthroline (Bphen) doped with rubidium carbonate (Rb2CO3) as electron injection layers were investigated. Current-voltage characteristics reveal that the devices with Bphen/Rb2CO3/Al as cathode structures possess better electron injection efficiency than those with cathode structures of Bphen/LiF/Al. Ultraviolet and x-ray photoemission spectroscopy shows that n-type doping effects resulting from Rb2CO3 and the gap states created by aluminum deposition are both keys to the improved carrier injection efficiency. Moreover, theoretical calculation indicates that the chemical reaction between aluminum and the nitrogen atoms in Bphen is the origin of the gap states.

Synthesis and characterization of Cp∗Rh (III) and Ir (III) polypyridyl complexes:: fluxional behaviour of Rh (III) complexes and molecular structure of [Cp∗Rh (Ph-terpy)Cl]BF4 complex (Cp∗=η5− (C5Me5))

Abstract Reaction of [Cp ∗ M( μ -Cl)Cl] 2 (Cp ∗ = η 5 - (C 5 Me 5 ), MRh, Ir) with 4′-phenyl-2,2′: 6′, 2″ terpyridine (Ph-terpy), L 1 and 1,4-bis (2,2′: 6′, 2″-terpyridin-4′-yl)benzene (diterpy), L 2 results in the formation of cationic complexes by the cleavage of halide bridge. These complexes, [Cp ∗ RhL 1 Cl]BF 4 , (1), [ (Cp ∗ RhCl) 2 L 2 ] (BF 4 ) 2 , (2), [Cp ∗ IrL 1 Cl]BF 4 , (3) and [ (Cp ∗ IrCl) 2 L 2 ] (BF 4 ) 2 , (4) are characterised by various spectral methods. Ph-terpy coordinates the metal ion in a bidentate fashion to form mononuclear complexes while diterpy bridges two metal ions to form dinuclear complexes. Complex (1) is crystallographically characterised. In solution Rh (III) complexes show fluxional behavior.

Synthesis, structure and magnetic properties of mononuclear [Mn(2,2′-bipyrimidine)2(H2O)2][ClO4]2 and polynuclear [Mn(2,2′-bipyrimidine)(NO3)2] complexes

Abstract Two new complexes [Mn(bpym)2(H2O)2][ClO4]2 (bd1) and [Mn(bpym)(NO3)2] (2) (bpym = 2,2′-bipyrimidine) have been prepared and characterized by spectroscopic and X-ray diffraction methods. Compound 1 consists of a mononuclear [Mn(bpym)2(H2O)2]2+ unit in which the manganese atoms shows a distorted elongated octahedral coordination with two bpym nitrogens and two H2O oxygens forming a cis configuration. The structure of compound 2 is made up of an infinite zigzag bpym-bridged polymeric chain with [Mn(bpym)(NO3)2] units, in which the manganese atom has seven coordination with four nitrogen atoms of two bpym ligands and three oxygen atoms of monodentate NO3− and bidentate NO3− anions. The intermetallic distance of Mn…Mn is 6.234(2) A. The temperature dependence of the magnetic susceptibility of 2 reveals the presence of a one-dimensional Heisenberg antiferromagnetic chain with J = −0.93 cmsu−1.

REINVESTIGATION OF THE CRYSTAL STRUCTURE AND CRYOMAGNETIC BEHAVIOUR OF COPPER(II) PROPIONATES

Abstract Two different complexes of copper(II) propionates, [Cu2(C2H5CO2)4] (1) and Na[Cu4(C2H5CO2)9(H2O)3] (2) have been isolated from the reaction of Cu(II)(NO3)23H2O with propionic acid in an aqueous solution of NaOH. X-ray structural analysis revealed that complex 1 consists of a one-dimensional chain of an apical-to-basal CuOCu linkage of pairwise binuclear anhydrous cupric propionates, which agrees with results previously reported. Compound 2 consists of a cation Na+ which interacts with six oxygen atoms of carboxylate groups, and anionic [Cu4(C2H5CO2)9(H2O)3]− ion, which contains one isolated syn-syn-carboxylato dimeric copper(II) complex [Cu2(C2H5CO2)4(H2O)2], and a linear chain containing one syn-syn-carboxylato dimeric [Cu2(C2H5CO2)4] and its apical position linked by a carboxylate bridge with a unit of [Cu(C2H5CO2)(H2O)]. Cryomagnetic susceptibilities 1 and 2 have been measured over the temperature range 4–300 K. In 1, the spins are coupled through an alternating one-dimensional antiferromagnetic interaction. In 2, the cryomagnetic exchange interaction has been interpreted in terms of a strong antiferromagnetic interaction associated with the two paired dinuclear units of Cu(II) ··· Cu(II), and one mononuclear Cu(II) unit which complies with a Curie-Weiss law.

Enhancement in current efficiency in organic light-emitting diodes with incorporation of subphthalocyanine

A highly efficient hole injection material, boron subphthalocyanine chloride (SubPc), was incorporated in organic light-emitting diodes. Device performance is greatly enhanced by inserting an ultrathin layer of SubPc between anodes and N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidene (NPB). Electronic structures and chemical reaction at the interface between NPB and SubPc are also investigated by photoemission spectroscopy with synchrotron radiation sources. Extra states are observed at the forbidden gap of SubPc with deposition of NPB, resulting from the broken bonds between boron and chlorine on SubPc with presence of NPB. These gap states are attributed to the improvement of device performance.

Synthesis and Characterization of Tetraosmium Carbonyl Complexes Containing a Bridging CO~2 Ligand

Treatment of (thd)H (thd=2,2,6,6-tetramethyl-3,5-heptandionate) with excess Os3(CO)12 in an autoclave at 180°C gives the formation of a brown metal chain complex [Os2(CO)5(thd)2]2 (1) and a yellow CO2 cluster complex [Os4(μ-H)(μ-CO2)(thd)(CO)13] (2) in low yields. Complex 2 was fully identified by a combination of spectroscopic methods and X-ray diffraction study, showing a unique CO2 ligand bridging a triosmium metal fragment, Os3(μ-H)(CO)10 and a monometallic osmium fragment, Os(CO)3(thd). Upon treatment of 1 with Me3NO at an elevated temperature, oxidation of the CO ligand occurred at the position trans to the unique CO2 ligand on the Os(CO)3(thd) fragment, giving the formation of a second CO2 cluster [Os4(μ-H)(μ-CO2)(thd)(CO)12(NCMe)] (3), which is stabilized by a weakly coordinated acetonitrile molecule.

Interfacial electronic structure of copper phthalocyanine on a gold surface studied by synchrotron radiation photoemission

We have studied copper phthalocyanine (CuPc) molecules deposited on a clean goldsurface via synchrotron radiationphotoemission. The persistent appearance of Au4f surface core-level emission in a series of depositions suggests columnar growth of the adsorbed molecules covering only one-fifth of the surface. Molecular adsorption reduced the line intensity of emission from the Ausurface slightly and also produced a shortened core-level shift, which demonstrates weakened s-d hybridization of the surface band. Moreover, manifestation of excess charge in the C1s core, along with an induced component in the Au4f core, indicates that charge polarization occurred at the organic/metal contact. The interface introduces an electronic state 1.09 eV below the Fermi level. Further analysis reveals that only the carbon atoms in the benzene rings are affected upon adsorption, suggesting that the molecular plane lies flat on the surface without changing the nominal bent configuration.