Efficient electroluminescent tertiary europium(III) β-diketonate complex with functional 2,2′-bipyridine ligand

A new red electroluminescent complex (2Fphen-bpy)Eu(DBM)₃(2Fphen-bpy: 4-(2,4-difluorophenylene)-2,2′-bipyridine; DBM: dibenzoylmethanate) was designed and synthesized. X-ray single crystal structural analysis shows that the dihedral angles involving the difluorophenylene moiety and two pyridine rings of the 2,2′-bipyridine unit in (2Fphen-bpy)Eu(DBM)₃ are 42° and 51.6°, indicant of non-conjugation between the two segments. The europium complex was incorporated into the doped electroluminescent device: ITO/TPD(40 nm)/(2Fphen-bpy)Eu(DBM)₃:CBP(30 nm, 3%)/BCP(20 nm)/Alq₃(30 nm)/LiF(1 nm)/Al(100 nm). At the brightness of 100 cd/m², the current and power efficiency are about 2.53 cd/A and 0.79 lm/W, respectively. In comparison with the inefficient control device using (2,2′-bipyridine)Eu(DBM)₃ as the red emitter in the same configuration, the introduction of difluorophenylene moiety into the Eu(III) complex could possibly account for the improved performance of the title compound.     

A binuclear aluminum(III) complex: Thermal stability,photophysical, electrochemical and electroluminescent properties

A novel binuclear aluminum(III) complex with acylpyrazolone derivative as ligands, bis(salicylidene-o-aminophenol)-bis(4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one)-bis-aluminum(III) [Al₂(saph)₂(PMBP)₂] was designed and synthesized. A detailed study was carried out on its thermal stability, photophysical, electrochemical and electroluminescent properties. It was found that the introduction of 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one (PMBP) ligands improved the thermal stability remarkably. Organic light-emitting diodes (OLEDs) based on this Al complex as the sole emitter and the host for red dopant were fabricated. Bright green-yellow emission was observed from the device using Al₂(saph)₂(PMBP)₂ as the emitter and the electron transporting layer. Pure red emission peaked at 632 nm was obtained from the Al₂(saph)₂(PMBP)₂ doped with DCJTB [4-(dicyanomethylene)-2-tertbutyl-6(1,1,7,7,-tetramethyljulolidyl-9-enyl)-4H-pyran] device with a luminance efficiency of 1.51 cd/A at 200 A/m². No light from Al₂(saph)₂(PMBP)₂ was found, indicating that the matched energy levels provide an efficient red emission system in Al₂(saph)₂(PMBP)₂ device. Those results demonstrated that Al₂(saph)₂(PMBP)₂ might be a promising material for OLEDs.     

Synthesis and photoluminescent properties of novel furopyrimidine derivatives

The novel furopyrimidine derivatives were synthesized and their photoluminescent properties were measured by UV–vis spectroscopy and luminescent spectroscopy. The compounds showed strong emitting properties in the range of 384 and 478 nm.     

Intermolecular energy transfer in photo- and electroluminescence properties of a europium(III) complex dispersed in poly(vinylcarbazole)

The photoluminescence (PL) and electroluminescence (EL) properties of Eu(TTA)₃Phen (TTA: thenoyltrifluoroacetonate; Phen: 1,10-phenanthroline) dispersed in poly(N-vinylcarbazole) (PVK) in multilayer organic light emitting diodes (OLEDs) have been investigated. Both Gd(TTA)₃Phen and tris(8-hydroxyquinoline) aluminum (Alq₃) were used as an electron transporting layer in order to compare their electron energy transfer properties in OLEDs.     

Synthesis,photophysical and electrophosphorescent properties of a novel fluorinated rhenium(I) complex

A novel fluorinated rhenium complex, i.e., Re-BFPP (BFPP, 2, 3-bis(4-fluorophenyl)pyrazino[2,3-f][1,10]phenanthroline) was designed, synthesized and characterized by ¹H NMR and mass spectroscopy. The light-emitting and electrochemical properties of this complex were studied. The organic light-emitting diodes (OLEDs) employing Re-BFPP as a dopant emitter with the structures of ITO/m-MTDATA (10 nm)/NPB (20 nm)/CBP: X wt.% Re-BFPP (30 nm)/Bphen (10 nm)/Alq₃ (30 nm)/LiF (1 nm)/Al (100 nm) were successfully fabricated and a broad electroluminescent peak at 553 nm was observed. The 10 wt.% Re-BFPP doped device exhibited the maximum luminance of 6342 cd/m² and a peak current efficiency of 17.9 cd/A, corresponding to the power efficiency of 8.1 lm/W.     

Synthesis, characterization, and electroluminescent properties of iridium complex containing 4-phenybenzoquinoline ligand

A phosphorescent iridium(III) complex Ir(PBQ)₂(acac) (PBQ: 4-phenylbenzoquinoline, acac: acetylacetone) was designed and synthesized, and the single crystal of this complex was obtained. This complex shows well optoelectronic properties. The organic light emitting devices (OLEDs) based on this complex were successfully fabricated with the device configuration of ITO/NPB or TCTA (40 nm)/Ir-complex: CBP (7%, 30 nm)/BCP (15 nm)/Alq (30 nm)/LiF (1 nm)/Al (100 nm). Using TCTA as the hole-transporting material, the device gives an extremely high external quantum efficiency of 14.6% at 5.0 V, a brightness of 61,693 cd/m² at 16.0 V, and a power efficiency of 37.0 lm/W at 3.5 V.     

Synthesis,photophysical and electroluminescent properties of a novel bright light-emitting Eu3+ complex based on a fluorene-containing bidentate aryl phosphine oxide

A novel bidentate aryl phosphine oxide (APO) ligand with fluorene as the chromophore (9,9-diethyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine)oxide (EFDPO), as well as the corresponding Eu³⁺ complex 1 were designed and synthesized. The strong absorption antennae effect of the functional APO ligands was proved. The effect of EFDPO in the intramolecular singlet and triplet energy transfer was also investigated. It is showed that the rigid structure and the appropriate energy levels of EFDPO not only reduce the energy loss induced by the structure relaxation, but also restrain the solvent quenching and facilitate the energy transfer from EFDPO to Eu³⁺. The thermal analysis was also performed to prove the improved thermal stability and phase stability of the complex. The complex exhibited good electroluminescent (EL) performance, such as maximum brightness more than 600 cd m^?2, E.Q.E. around 2% and stable monochromic red emission at 616 nm.     

Synthesis and electroluminescent properties of heterocycle-containing poly(p-phenylene vinylene) derivatives

Two novel conjugated polymers were synthesized by the Wittig reaction. The multilayer light emitting diodes were fabricated and showed green to blue electro-luminescence.     

Synthesis,optical and electrochemical properties of novel hole-blocking poly(biphenylene-1,3,4-oxadiazole) containing electron-withdrawing trifluoromethyl groups

New poly(biphenylene-1,3,4-oxadiazole) P1 and poly(biphenylene hydrazide) P2 containing electron-withdrawing trifluoromethyl group at the 2 and 2′ positions of biphenyl moiety were synthesized. The biphenyl is forced to adapt a non-coplanar conformation due to the bulky trifluoromethyl group. High quality polymer P1 thin film can be easily obtained by thermal cyclodehydration from its soluble polyhydrazide precursor P2. The polymer P1 exhibited good thermal stability with glass transition temperature of 234 °C and 5% decomposition temperature of 469 °C. The optical and electrochemical properties were investigated by UV–vis spectroscopy, photoluminescence spectroscopy and cyclic voltammetry. For polymer P1 film, two absorption peaks at 370 and 414 nm were observed. It also exhibited a photoluminescent peak at 555 nm when excited by 414 nm light. The cyclic voltammetric studies revealed that polymer P1 had extremely low HOMO (?6.85 eV) and LUMO (?3.71 eV) energy levels due to the presence of strong electron-withdrawing trifluoromethyl group. It also exhibited a large energy gap (3.14 eV) which is an indication of short conjugation length resulted from non-coplanar biphenyl structure. Its HOMO energy was even lower than that of widely used hole-blocking material, 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole PBD (?6.30 eV). The low LUMO energy of polymer P1 could allow the easier electron injection from air-stable cathode such as aluminum. The good electron transfer ability was also shown by measuring the current density of electron-only devices with the structures of Al/P1 (150 nm)/Alq₃ (50 nm)/Al and Al/Alq₃ (200 nm)/Al. Combined with high thermal stability and amorphous morphology, polymer P1 would be a promising candidate as the hole-blocking material for organic light-emitting diodes.     

Synthesis and electrochemical,electrochromic and electrical properties of novel s-triazine bridged trinuclear Zn(II), Cu(II) and Lu(III) and a tris double-decker Lu(III) phthalocyanines

The new s-triazine-bridged trinuclear Zn(II) and Cu(II) phthalocyanines have been synthesized from the reaction of corresponding anhydrous metal salts, Zn(OAc)₂ and CuCl with 4,5-bis(hexylthio)-phthalonitrile and 2,4,6-tris(2-thiophthalonitrile)-s-triazine. The tris phthalonitrile derivative of s-triazine was prepared from the reaction of 4-nitrophthalonitrile and thiocyanuric acid in dry dimethylformamide as solvent using K₂CO₃ as the base. The same route was applied to prepare the trinuclear Lu(III) phthalocyanine analogue. The conversion of tris phthalonitrile into its isoindoline derivative was accomplished by bubbling ammonia gas through a solution in methanol in the presence of sodium methoxide. The cyclization of two different isoindoline derivatives and 4,5-bis(hexylhthio)-1,2-diiminoisoindoline, with lutetium (III) acetate in dimethylformamide gave trinuclear Lu(III) phthalocyanine. The reaction of this complex with octakis-hexylthio phthalocyanine led to the isolation of tris double-decker Lu(III) phthalocyanine. The structures of the target compounds were confirmed by elemental analysis, UV–vis, IR and MALDI-TOF mass spectroscopies. The d.c. and a.c. conductivities of the phthalocyanine compounds were measured as a function of temperature. The small value of pre-exponential factor suggested the conduction by localized states in the band tails and by localized states near the Fermi level. The temperature dependence of the frequency exponent showed that the conduction in these compounds is due to hopping of charge carriers. The tris double-decker phthalocyanine complex showed well-defined electrochromic behaviour with green-blue and blue-purple colour transitions.     

A novel Re(I) complex with oxdiazole moiety: Synthesis,characterization, photo- and electro-luminescence properties

In this paper, we report a novel phosphorescent Re(I) complex of Re(CO)₃(OP)Br, where OP = 2-(5-phenyl-[1,3,4]oxadiazol-2-yl)-pyridine, including its photophysical properties, geometric/electronic structures, electrochemical and thermal properties. Experimental data suggest that Re(CO)₃(OP)Br is a promising yellow emitter peaking at 545 nm with short excited state lifetime of ～0.06 μs. The Re(I) center localizes in a distorted octahedral field in Re(CO)₃(OP)Br and the emissive state of Re(CO)₃(OP)Br has metal-to-ligand-charge-transfer character, leading to the room-temperature phosphorescence. Further analysis reveals that Re(CO)₃(OP)Br has HOMO and LUMO energy levels at ?5.90 V and ?3.57 V respectively, as well as its high thermal decomposition temperature of 380 °C. Using Re(CO)₃(OP)Br as a dopant, an electroluminescence peaking at 560 nm is realized, with a maximum luminance of 4300 cd/m² and a maximum current efficiency of 11.3 cd/A.     

Synthesis,photo- and electroluminescent properties of norbornene based platinum-containing copolymers

Norbornene based monomers containing the 2-phenylpyridinato–N,C²′ platinum(II) complex bonded by acetylacetonate or pyrazolonate anchor groups were synthesized and copolymerized with a carbazole-containing norbornene comonomer by ring-opening metathesis polymerization (ROMP). The photo- and electroluminescence spectra of the resulting Pt-copolymers are similar. They consist of broad bands with maxima at 495, 530 and 565 nm which arise from the mixed ligand centered (LC) and metal to ligand charge transfer (MLCT) transitions. The copolymer with the cyclometalated platinum(II) complex bonded to the polymer chain via the pyrazolonate anchor group revealed the highest brightness of electroluminescence (260 cd/m² at 21 V).     

Synthesis and properties of μ-cyano(phthalocyaninato)-rhodium(III)

This contribution reports on the synthesis of μ-cyano(phthalocyaninato)rhodium(III), [PcRhCN]_n (1), by splitting off potassium cyanide from potassium(dicyano)phthalocyaninatorhodium(III), K[PcRh(CN)₂] (2). Monomeric complexes, PcRh(L)CN (7), were formed when [PcRhCN]_n (1) was treated with base molecules L, such as n-butylamine and pyridine. All compounds were characterized by IR, far-IR spectroscopy, thermal and elemental analyses, and partly by UV, ¹H-NMR and FD (field desorption) mass spectroscopy. The undoped polymer [PcRhCN]_n (1) exhibits a d.c. dark conductivity of 4 × 10^?4 S/cm, which was diminished by eight orders of magnitude when the polymeric structure was decomposed by treatment with a competing ligand.     

Synthesis and characterization of new electroluminescent poly(p-phenylene) derivative

A new electroluminescent poly(p-phenylene) (PPP)-type polymer (CHALC-PPP) incorporating chalcone-type groups as side-chains has been synthesized via a chemical modification of a precursor acyl-functionalized polymer. The chemical structure of the polymer was characterized by ¹H NMR, ¹³C NMR, and FT-IR spectroscopic analysis. CHALC-PPP contains a substitution ratio of 40% of vinylaryl groups. It is fully soluble in common organic solvents and has a number–average molecular weight of 3750 g/mol. CHALC-PPP thin solid film absorbs in UV and emits in the green region with a maximum at 512 nm. From the cyclic voltammetry analysis, the HOMO and LUMO energies levels values are ?5.67 and ?2.70 eV, respectively. A multilayer diode device with the configuration ITO/PEDOT:PSS/CHALC-PPP/BCP/Al emitting a green light has been fabricated.     

Synthesis,characterization, mesomorphic and electrical properties of tetrakis(alkylthio)-substituted lutetium(III) bisphthalocyanines

The synthesis of new lutetium(III) bisphthalocyanines substituted with alkylthio groups (1–5) is described. These compounds (Pc₂Lu) are soluble in most common organic solvents and have been fully characterized (elemental analysis, FT-IR, UV–Vis spectroscopy, mass spectrometry). The thermal stabilities of the Pc compounds were determined by thermogravimetric analysis (TGA). The mesogenic properties of these new materials forming columnar-hexagonal (Col_h) mesophases were studied by differential scanning calorimetry (DSC), optical microscopy and X-ray diffraction. The compounds 2–5 exhibit a double clearing point. DC electrical properties of these compounds in different phases were determined by measuring I–V characteristics and dark current of their thin films on interdigital electrodes. The measurements were carried out in ambient air, in vacuum and in high purity nitrogen (N₂) flow in the temperature range between 300 and 420 K. Dark current measurements obtained in the crystal, liquid crystal (LC) and isotropic liquid phases were in agreement with the phase transitions of these compounds obtained by DSC and optical microscopy results. The relation between the phase transition and conductivity of the Pc₂Lu derivatives were investigated. Also, the influence of the nature of the substituted group (alkylthia and alkoxy) upon the DC electrical properties of the Pc₂Lu derivatives was investigated. The DC conductivities and the thermal activation energies depending on alkyl chain lengths of these compounds were found to be in the range of 10^?8 to 10^?5 S/cm and 0.12–0.38 eV in solid phase.     

Synthesis,photophysics, electrochemical and electroluminescent properties of divinylene compounds with phthalimide moieties

Three new divinylene compounds F, C and P which contained fluorene, carbazole and phenylene as central unit, respectively, and terminal phthalimide groups were synthesized by Heck coupling. The alkyl or alkoxy chains attached to the central unit as well as the cyclohexyl ring attached to the terminal phthalimides render the samples very soluble in common organic solvents. They had relatively low glass transition temperatures (T_g's), being in the range of 54–81 °C. P was stable up to about 200 °C while F and C were stable up to 300 °C. The absorption maximum was located at 387–440 nm with optical band gap of 2.48–2.56 eV. They emitted blue-green light with emission maximum at 484–562 nm. P showed the most red-shifted absorption and emission maximum. The HOMO and LUMO levels of the compounds, estimated from their cyclic voltammograms, were −6.42 to −5.58 eV and −3.06 to −2.99 eV, respectively, from which their band gaps were estimated to be 3.36 eV, 2.68 eV, and 2.52 eV. The emission spectra and performance of the EL devices, using blends of the compounds and PVK as emitting layer, also depended strongly on the compounds. The P device emitted green light (530 nm) with maximal luminance and current efficiency being at 1358 cd/m² and 0.57 cd/A, while those of the F device were green-blue (490 nm), 593 cd/m² and 0.22 cd/A.     

Interaction of the europium chloride and polyaniline: formation of a novel conductive complex

A novel polyaniline (PANI):EuCl₃ complex has been prepared and its conductivity, electronic absorption and luminescent spectra were studied. Changes in electronic absorption spectra showed that the europium ions possess both oxidative and pseudoprotonation activity with respect to the polymer chains in solution and solid films, respectively. Photoluminescence (PL) spectra showed that the charge transfer from the polymer to Eu³⁺ ions occurs and that there are two types of europium luminescent centers in the disordered polymer matrix. Electrical conductivity of the composite films with a stoichiometric ratio of PANI to the europium salt was found to be unexpectedly high and comparable with that of the protonic acid doped PANI. Mechanisms of the PANI:EuCl₃ complex formation are discussed.     

Synthesis,optical and electroluminescent properties of an alternating copolymer of triphenylamine and fumaronitrile

A new conjugated alternating copolymer of triphenylamine and fumaronitrile, TPA–FN, was synthesized via Heck coupling reaction and characterized by GPC, UV–vis, ¹H NMR and elemental analysis. The polymer film showed two absorption peaks at ca. 370 nm and 500 nm, respectively, and a narrow bandgap of 1.72 eV. The photoluminescence spectrum of TPA–FN film displayed a main peak at ca. 724 nm and a shoulder peak at ca. 808 nm, indicating that the polymer could be a near-infrared luminescent polymer. Cyclic voltammetry measurements revealed a lower LUMO energy level of TPA–FN at −3.85 eV. The lower LUMO level could be ascribed to the introduction of the electron-withdrawing fumaronitrile with two cyano groups attached to trans-vinylene, and it favors the electron injection for the application in the polymer light-emitting diodes (PLEDs). A single-layer PLED based on TPA–FN was fabricated and the device showed the turn-on voltage of 6 V and the maximum luminance of 136 cd/m² at 11.5 V.     

Triphenylamine- and oxadiazole-substituted poly(1,4-phenylenevinylene)s: synthesis,photo-, and electroluminescent properties

Novel triphenylamine- and oxadiazole-substituted poly(1,4-phenylenevinylene)s (PPV) or CN-PPV (P1–4) were synthesized by the Wittig–Horner, Knoevenagel, and Gilch type polymerization. The polymers exhibited good solubility in common organic solvents, relatively high photoluminescent (PL) efficiency, and high HOMO level for ca. −5.1 eV. The simple double-layer devices of triphenylamine-PPV (P1), ITO/PEDOT: PSS/P1/Cs/Al, exhibited a very high luminance of 510 cd/m² under a low driving voltage of 3 V, demonstrating the effectiveness of triphenylamine moiety as a substituent of PPV derivatives for a light-emitting polymer. Triphenylamine-CN-PPV (P2) exhibited bipolar reversible redox in CV. The bipolar type of PPVs, P2 and triphenylamine-oxadiazole-PPV (P3), showed lower luminance and efficiency than those of the p-type of PPV (P1).