Efficient red organic light-emitting devices based on a europium complex

An efficient organic light-emitting device using a trivalent europium (Eu) complex Eu(Tmphen)(TTA)(3) (TTA=thenoyltrifluoroacetone, Tmphen=3,4,7,8-tetramethyl-1,10-phenanthroline) as the dopant emitter was fabricated. The devices were a multilayer structure of indium tin oxide/N,N-diphenyl-N,N-bis(3-methylphenyl)-1,1-biphenyl-4,4-diamine (40 nm)/ Eu complex:4,4-N,N-dicarbazole-biphenyl (1%, 30 nm)/2,9-dimethyl,4,7-diphenyl-1,10phenanthroline (20 nm)/AlQ (30 nm)/LiF (1 nm)/Al (100 nm). A pure red light with a peak of 612 nm and a half bandwidth of 3 nm, which is the characteristic emission of trivalent europium ion, was observed. The devices show the maximum luminance up to 800 cd/m(2), an external quantum efficiency of 4.3%, current efficiency of 4.7 cd/A, and power efficiency of 1.6 lm/W. At the brightness of 100 cd/m(2), the quantum efficiency reaches 2.2% (2.3 cd/A).

A cunning strategy in design of polymeric nanomaterials with novel microstructures

A relative approach, based on the dynamic density functional theory, for simulating the solvent evaporation rate dependence of self-assembly process of block copolymers in solution is proposed. The di- and triblock copolymers are first chosen as the candidates for exploration of novel microstructures. The results reveal that asymmetrical block copolymers with unequal block length, which generally exhibit disordered microdomain patterns in melts, have the ability to assemble into periodic ordered microdomain patterns by properly controlling solvent evaporation rate, e.g., diblock copolymers may assemble into lamellar microstructures with lamellar thickness proportional to individual block length. This simulation suggests a strategy of design and manufacture of polymeric nanomaterials with novel microstructures.

Blue organic light-emitting devices with an oxadiazole-containing emitting layer exhibiting excited state intramolecular proton transfer

We report a blue organic light-emitting device having an emissive layer of 2-(2-hydroxyphenyl)-5-phenyl-1,3,4-oxadiazole (HOXD), that exhibits excited state intramolecular proton transfer (ESIPT). The device had a luminance efficiency of 0.8 cd/A and a maximum brightness of 870 cd/m(2). Electroluminescence spectra revealed a dominating peak at 450 nm and two additional peaks at 480 and 515 nm with a full width at half maximum of 50 nm. Our studies indicate that some EL may originate from the triplet excitation state of the enol form of HOXD.

Interactions of thiamine monophosphate (TMP) with one- and two-dimensional polymeric halogenomercurate anions. Crystal structures of (TMP)(Hg2Br5)center dot 0.5H(2)O and (TMP)(2)(Hg3I8)

An investigation into the interactions between thiamine monophosphate (TMP) and anions has resulted in the preparation and X-ray characterization of the compounds (TMP)(Hg2Br5).0.5H(2)O (1) and (TMP)(2)(Hg3I8) (2). In each compound the TMP molecule exists as a monovalent cation in the usual F conformation. The halogenomercurate anions occur in two-dimensional (2-D) network in 1 or one-dimensional (1-D) chain in 2. In both 1 and 2, the structures consist of alternating cationic sheets of the hydrogen-bonded TMP molecules and anionic sheets of the polymeric halogenomercurate anions. The TMP molecule binds to the polymeric anions through the characteristic 'anion bridge I', C(2)-H..X...pyrimidinium (X = Br in 1 and 1 in 2), and electrostatic interactions between electropositive S(1) and halogen atoms. The 'anion bridge II' of the type N(4'1)-H...X...thiazolium (X = phosphate group) plays a role in stabilizing the molecular conformation. The biological implication of the host-guest-like complexation between TMP and polymeric anions is discussed.

Oriented polyoxometalate-polycation multilayers on a carbon substrate

In this paper, a new method of fabricating multilayers on a carbon substrate is presented. First, a uniformly charged carbon surface was prepared through molecular design. Then an ultrathin film consisting of layer-pairs of oppositely charged polymeric cationic poly(diallyldimethylammonium chloride) (PDDA) and silicotungstate, SiW12O404- (SiW12), was grown layer-by-layer onto the grafted carbon substrate using a molecular self-assembly technique and an electrochemical method. The technique allows one to prepare highly adherent, dense and smooth films of polyoxometalates with special properties. By combining cyclic voltammetry (CV) and X-ray (XR) reflectometry, it was determined that the average surface density of SiW12 was 2.10 x 10(-10) mol cm(-2), and the thickness increase per adsorption of PDDA-SiW12 was 1.7 +/- 0.2 nm, indicating that the amount of SiW12 anion per one layer adsorption corresponded to a monolayer coverage. Atomic force microscopy (AFM) was also used to examine the surface morphology and determine the grain size distribution and roughness for multilayer films. An increase in root-mean-square (RMS) surface roughness from 7 to 9 Angstrom was observed as the number of layer-pairs in the film increased from 2 to 6. FTIR results showed that the good stability of the multilayer films was due to Coulomb interactions between the SiW12 anion and the polymeric cations PDDA. Moreover, the multilayer films, in acidic aqueous solution, showed good electrocatalytic activity toward the reduction of NO2-, and the catalytic currents increased with increasing the layer numbers of SiW12 adsorption. These characteristics of the multilayer films might find potential applications in the field of sensors and microelectronics devices.

Methods to study the ionic conductivity of polymeric electrolytes using a.c. impedance spectroscopy

Composite polymeric electrolytes of PEO-LiClO4-Al2O3 and PEO-LiClO4-EC were prepared and the ionic conductivity by a.c. impedance was calculated using four different methods, and three kinds of representations of a.c. impedance spectra were adopted. The first is based on the Nyquist impedance plot of the imaginary part (Z") versus the real part (Z') of the complex impedance. The second and the third correspond to the plots of imaginary impedance Z" as a function of frequency (f), and the absolute value (\Z\) and phase angle (theta) as a function of f, respectively. It was found that the values of the ionic conductivity calculated using the three representations of a.c. impedance spectra are basically identical.

Synthesis and properties of alternating copolymers containing PPV and hole-transporting units for light-emitting devices

A series of alternating copolymers containing triphenylamine (TPA) moieties and oligomeric PPV segments in the main chain have been synthesized by Wittig condensation. The resulting polymers exhibit good thermal stability with decomposition temperatures (Tds) above 305 degreesC under nitrogen at 10 degreesC/min, and high glass transition temperatures (Tgs). They show intense photoluminescence in solution and film. The single-layer electroluminescent device using TAA-PV1 as emissive layer emits green light at 522nm with a turn-on voltage of 6V and maximum brightness of about 200cd/m(2) at 20V.

Effects of the morphologies and structures of light-emitting layers on the performance of organic electroluminescent devices

Organic electroluminescent devices with a structure of ITO/ploy (9-vinylcarbazole)/tris (8-hydroxyquinoline) aluminum (Alq3)/Mg:Ag are fabricated at different substrate temperatures (77, 298, and 438 K) during Alq3 deposition. It is found that the surface morphologies of Alq3 thin films greatly affect the I-V characteristics of the devices by the contact area between metal cathode and light-emitting layer. There is an increase in the luminous efficiency of the devices in the order 77 K < 298 K < 438 K. We attribute this trend to different structures of Alq3 thin films. (C) 2001 American Institute of Physics.

Electrochemical preparation and characterization of silicotungstic heteropolyanion monolayer electrostatically linked aminophenyl on carbon electrode surface

In this paper, an organic-inorganic composite film of heteropolyanion was Formed by attaching a Keggin-type heteropolyanion, SiW12O404-, on carbon electrode surface derivatized by 4-aminophenyl monolayer. The composite film thus grafted on carbon electrode surface has good stability because of the ionic bonding character between SiW12O404- and surface aminophenyl groups. X-ray photoelectron spectroscopy, scanning tunneling microscopy, and cyclic voltammetry were used to characterize the composite film. Compared with SiW12O404- electrodeposited on a bare glassy carbon electrode (GCE), the composite film gives three more sharp and well-defined redox couples attributed to two one- and two-electron processes, and the analyses of the voltammograms of SiW12O404- anion in the composite film modified on GCE shows that its surface coverage is close to a closest packing monolayer. STM characterization shows that a two-dimensional order heteropolyanion monolayer was formed on HOPG substrate. The composite film provides a favorable environment for electron and proton transfer between SiW12O404- ion and electrode surface, which may make it suitable for various applications in sensors and microelectronics devices.

Bright green organic electroluminescent devices based on a novel thermally stable terbium complex

A navel thermally stable terbium carboxylate complex, Tb(MTP)(3)(phen) (MTP=monotetradecyl phthalate, phen=1,10-phehanthroline), was synthesized and characterized. The device structure of glass substrate/indium-tin-oxide/poly(p-phenylenevinylene) (PPV)/poly (N-vinycarbazole) (PVK):Tb(MTP)(3)(phen): 1,3,4-oxadizole derivative (PBD)/tris(8-hydroxyquinoline) (Alq(3))/aluminum (Al) was employed to study the electroluminescent properties of Tb(MTP)(3)(phen). A green emission with extremely sharp spectral band of less than 10 nm at 544 nm peak wavelength was observed. A maximum luminance of 152 cd/m(2) and an external quantum efficiency of 0.017% were achieved at a drive voltage of 24 V. A possible mechanism of energy transfer based on the polymer doped with lanthanide organic complex was also proposed.

Lanthanide coordination polymers with dicarboxylate-like ligands: crystal structures of polymeric lanthanum(III) and terbium(III) complexes with flexible double betaines

Four novel polymeric lanthanide(III) complexes of two new double betaine derivatives have been synthesized and structurally determined. In [{La-2(L-1)(2)(H2O)(9)}(n)]Cl-6n. 2nH(2)O (1) and [{Tb(L-1)(H2O)(4)}(n)]Cl-3n. nH(2)O (2) (L-1 =4,4'-trimethylenedipyridinio-N,N'-diacetate), the lanthanide(III) ions form a two-dimensional layer in which each pair of lanthanide(III) ions is bridged by two syn-anti mu-carboxylato-O,O' groups. Adjacent layers are cross-linked through hydrogen bonds among aqua ligands, lattice water molecules and chloride ions, to form a three-dimensional network. Isomorphous [{Ln(L-1)(H2O)(4)}(n)]Cl-3n. 5nH(2)O (Ln=La, 3; Ln=Tb, 4; L-2=1,3 bis(pyridinio-4-carboxylato)-propane) each contain a centrosymmetric paddle-wheel-like dimeric unit in which each pair of adjacent metal atoms is bridged by four syn-syn mu-carboxylato-O,O' groups that are oriented nearly perpendicular to each other about the metal-metal axis. Neighboring dimeric subunits are bridged by a pair of flexible LL ligands into a polymeric chain. Adjacent chains are inter-linked by hydrogen bonds among aqua ligands, lattice water molecules and chloride ions into a three-dimensional network. (C) 1999 Elsevier Science Ltd. All rights reserved.

Synthesis and crystal structure of a polymeric erbium(III)-sodium(I) coordination complex of picolinic acid N-oxide

A new Er(III)-Na(I) coordination polymer of stoichiometry [NaEr2L5(H2O)(6)(NO3)](NO3). 3.5H(2)O (HL = picolinic acid N-oxide) has been synthesized and characterized by single-crystal X-ray analysis. Crystals are triclinic, P (1) over bar with a = 9.823(2), b = 12.453(2), c = 20.643(4) Angstrom; alpha = 98.49(3), beta = 101.40(3), gamma = 108.69(3)degrees; V = 2284(1) Angstrom(3); Z = 2. Of the two independent eight-coordinate erbium(III) ions in this complex, one is surrounded by four bidentate chelating L ligands, and the other by one bidentate chelating L ligand, four aqua ligands and two anti-carboxylate oxygen atoms from two neighboring [ErL4] units. The sodium(I) ion is in a distorted octahedral environment, being coordinated by a unidentate nitrate anion, three aqua ligands and two anti-carboxylate oxygen atoms from two adjacent [ErL4] units. The complex is built from zigzag chains of syn-anti carboxylate-bridged erbium(III) moieties directed in the a direction, which are cross-linked pairwise by aqua-bridged dimeric sodium(I) units. The resulting composite polymeric chains are further connected by hydrogen bonds to form a three-dimensional network.

Bright red organic electroluminescent devices based on a soluble rare earth complex Eu(TTA)(3) Phen

An Electroluminescent device with PVK film doped with Eu(TTA)(3) Phen and PBD was fabricated. The device structure of glass substrate/indium-tin-oxide/PPV/PVK : Eu(TTA)3 Phen : PBD/Alq(3)/Al was employed. A sharply red electroluminescence with a maximum luminance of 56. 8 cd/m(2) at 48 V was achieved.