Photo- and electro-luminescent properties of thermotropic liquid crystalline quaterphenyl analogues comprising a 2,2'-bi-1,3,4-thiadiazole unit

Thermotropic liquid crystalline quaterphenyl analogues constituting a central 2,2'-bi-1,3,4- thiadiazole ring, the compounds 5,5'-bis(4-methoxy- and 4-octyloxy-phenyl)-1,3,4-thiadiazole, have been prepared and their photoluminescent (PL) and electroluminescent (EL) properties evaluated. The materials form enantiotropic smectic and nematic phases. The PL spectra showed that they emit blue and green fluorescence in the solid state. The octyloxy compound exhibited an EL spectrum with blue emission and is a candidate for organic EL applications.     

2,5-二[4-(2-芳基乙烯基)苯基]噁二唑的合成及发光特征

二乙烯联苯及其衍生物是一种可发射蓝光的小分子空穴型有机发光材料, 通过Wittig-Horner反应, 将电子传输型噁二唑环“嵌入”其中, 设计合成了6个2,5-二[4-(2-芳基乙烯基)苯基]-1,3,4-噁二唑化合物. 经光谱分析和元素分析等方法确认了它们的化学结构. IR和UV-vis分析数据表明标题化合物分子结构中的C＝C双键均为反式结构特征. 研究结果表明: 2,5-二[4-(2-对二甲氨基苯基乙烯基)苯基]-1,3,4-噁二唑具有良好的蓝色发光性能; 取代基对标题化合物的UV-vis吸收光谱和发光特性的影响显着.     

Electrical properties of 1,4-bis(4-(phenylethynyl)phenylethynyl)benzene and its application for organic light emitting diodes

We found that a phenylene ethynylene derivative, 1,4-bis(4-(phenylethynyl)phenylethynyl)benzene (BPPB), provides very high photoluminescence efficiency both in solution (Phi(PL) = 95 +/- 3%) and thin films (Phi(PL) = 71 +/- 3%); further, we observed blue electroluminescence (EL) of lambda(EL(max)) approximately 470 and 510 nm with an external EL efficiency of eta(EL) approximately 0.53% and maximum luminance of approximately 70000 cd m(-2) at current density of approximately 2 A cm(-2) with BPPB as an emitter; also we identified that BPPB functions as a hole transport layer in organic light emitting diodes.     

Synthesis and photophysical characteristics of 2,7-fluorenevinylene-based trimers and their electroluminescence

Three new 2,7-fluorenevinylene-based trimers were synthesized and characterized. The synthesis was carried out by the Heck coupling reaction of 9,9-dihexyl-2,7-divinylfluorene with 2-(4-bromophenyl)-5-phenyl-1,3,4-oxadiazole, N,N-diphenyl-4-bromoaniline, or 3-bromopyrene to afford the trimers OXD, TPA, and PYR, respectively. All the trimers were readily soluble in common organic solvents such as tetrahydrofuran, dichloromethane, chloroform, and toluene. Their glass transition temperatures ranged from 33 to 60 degrees C. The UV-vis spectra showed an absorption maximum at lambda(a,max) = 379-417 nm with optical band gap of Eg = 2.47-2.66 eV. In solution, they emitted strong blue-green photoluminescence (PL) with PL maximum at lambda(f,max) = 455-565 nm and fluorescence quantum yield of Phi(f) = 0.65-0.74. On the other hand, in their spin-coated films, the PL efficiencies significantly decreased due to the presence of concentration quenching. All samples showed nanosecond transient lifetime containing two components, suggesting excimer formation. The organic light-emitting diodes (OLEDs) with OXD and TPA showed green emission with electroluminescence (EL) quantum efficiencies of eta(EL) approximately 10(-2)%, while very weak EL efficiency of eta(EL) approximately 10(-5)% was observed with PYR. The highest occupied molecular orbital (HOMO) levels of the films were found to be 5.05-5.75 eV.     

Photoluminescence and Electroluminescence Properties of 2,5-Bis[2,2′-bis(5-phenyl)-1,3,4-oxadiazole] Thiophene(T-OXD)and T-OXD/Poly(9-vinylcarbazole) Blends

The photoluminescence(PL) and the electroluminescence(EL) properties of a novel organic compound, 2,5-bis(2,2′-bis(5-phenyl)-1,3,4-oxadiazole(T-OXD), were studied in chloroform and in a solid thin film. The PL and the EL properties of T-OXD/poly(9-vinylcarbazole)(PVK) blends were also studied, which contained various contents of T-OXD. The PL maximum emission peaks of T-OXD/PVK blends show gradual bathochromtic-shift with the increase of the T-OXD content. The EL spectra of T-OXD/PVK devices are similar to their PL spectra, and all the EL maximum emission peaks show bathochromtic-shift compared with the corresponding PL spectra, which is ascribed to the formation of electroplex. The turn-on voltages for ITO/T-OXD:PVK/Al devices decreased from 13.5 V of the device cotaining 0.1% T-OXD(mass fraction) to 5 V of the device containing 5% T-OXD, which suggests that T-OXD improves the energy level match between T-OXD and PVK and enhances the emission efficiency. The experimental results indicate that T-OXD can be used as a good electron transporting material.     

New poly(p‐phenylene vinylene) derivatives with two oxadiazole rings per repeat unit: Synthesis,photophysical properties,electroluminescence, and metal ion recognition

Two new poly(p‐phenylene vinylene) derivatives OX1‐PPV and OX2‐PPV bearing two 1,3,4‐oxadiazole rings per repeat unit and a fully conjugated backbone with solubilizing dodecyloxy side groups were synthesized and investigated. The amorphous conjugated polymers had glass‐transition temperature values of 60–75 °C and emitted intense blue or greenish‐blue light in solution with photoluminescence (PL) emission maxima at 379–492 nm and PL quantum yields of 0.41–0.52. In the solid state they emitted yellowish‐green light with PL emission maxima at 533–555 nm. Cyclic voltammetry showed that both conjugated polymers had reversible reduction and irreversible oxidation, making them n‐type materials. The electron affinity of OX2‐PPV was estimated as 2.85 eV whereas that of OX1‐PPV was 2.75 eV. Yellow electroluminescence (EL) was achieved from single‐layer light‐emitting diodes of OX2‐PPV with an EL emission maximum at 555 nm and a brightness of 70 cd/m². Polymer OX2‐PPV, which was functionalized with 2,6‐bis(1,3,4‐oxadiazole‐2‐yl)pyridine, demonstrated sensitivity to various metal ions as a fluorescence‐mode chemosensor. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2112–2123, 2004     

新型p-/n-掺杂型交替共聚物的合成及其光电性能的研究

本文通过Heck偶联法制备一种新型p-/n-掺杂型电致发光材料--3-十二烷氧基噻吩-共-1,3,4-噁二唑交替聚合物(P3DDOTV-OXD), 用核磁共振（1H NMR）及凝胶色谱（GPC）对结构进行了分析表征。用紫外光谱（Uv-vis）、荧光光谱法及电化学分析法对其光电学性能进行了研究。结果表明：聚合物的重均分子量为：5287,在氯仿溶液中,聚合物的紫外最大吸收波长为314nm,在401nm处发射出明亮的蓝光;较其均聚物（516nm）蓝移了115nm。 循环伏安测定结果表明: P3DDOTV-OXD在正、负向区域分别出现了一对氧化还原峰对,电子亲和能（Ia）为：2.88eV,有利于电子从阴极的注入。3-十二烷氧基噻吩-共-噁二唑交替共聚物实现了集空穴、电子双向传输为一体的高性能的聚合物光电功能材料的性能要求。     

含噻吩单元的硅芴共聚物的合成及其蓝色电致发光性能

将少量(摩尔分数为1%—3％)含噻吩的窄带隙单体和宽带隙硅芴单体进行共聚, 合成了聚{9,9-二己基-3,6-硅芴-co-[2,5-二(2-甲基苯撑-4-基)-噻吩]}和聚{9,9-二己基-3,6-硅芴-co-[2,5-二(2-苯撑-4-基)-噻吩]}两类硅芴共聚物, 通过紫外-可见吸收光谱、光致发光光谱, 并制作聚合物发光二极管器件测试电致发光光谱等手段, 系统表征了两类硅芴共聚物材料的性能. 实验结果表明, 噻吩的加入形成了新的蓝色发光中心, 并且实现了从硅芴链段到含噻吩发光中心的有效能量转移. 通过增加发光中心结构的空间位阻来减小其共轭程度, 可以使聚合物的PL和EL光谱发生较大蓝移. 最终得到了效率为0.46%和色坐标(CIE)为(0.19, 0.16)的蓝光LED器件.     

Thermotropic liquid crystalline polymers containing five-membered heterocyclic groups IX. Synthesis and optical properties of liquid crystalline semi-rigid polyesters composed of a quinquephenyl analogue containing 1,3,4-thiadiazole and aliphatic chains

Novel semi-rigid polyesters containing a quinquephenyl analogue containing 1,3,4-thiadiazole and a central 1,3-phenylene unit in the main chain were synthesized by high temperature solution polycondensation of a dimethyl ester derivative of 1,3-bis(5-phenyl-1,3,4-thiadiazol-2-yl)benzene with an aliphatic (octa-, deca- and dodecamethylene) diol. The proposed structures were confirmed using FTIR and ¹H NMR spectroscopies, and elemental analyses; their liquid crystalline and photoluminescent (PL) properties were examined by means of differential scanning calorimetry, optical texture observations using polarizing microscopy, powder X-ray diffraction, and UV-vis and PL spectra measurements. These measurements showed that the polymers not only show a monotropic solid smectic or disordered crystal phase, but also PL properties with blue emission in HFIP solutions and in the solid phase, Stokes shifts of 116.5-119 nm being observed.     

LINEAR AND HYPERBRANCHED POLYMERS WITH HIGH THERMAL STABILITY AND LUMINESCENCE EFFICIENCY

New acetylene monomers, 6-{[(1-naphthylethynyl-4-phenyl)carbonyl]oxy}-1-pheny-1-hexyne (1), 2, 5-diethynyl-thiophene (3), and 4,4'-diethynylbiphenyl(6) were synthesized. Homopolymerization of 1 and copolycyclotrimerizations of 3and 6 with 1-heptyne and 1-octyne have been achieved with WCl_6- and TaCl_5-Ph_4Sn catalysts, respectively, giving solublelinear disubstituted polyacetylene (2) and hyperbranched polyarylenes (5 and 8) with high molecular weights (up to 1.2×10~5) in high yields (up to 98%). The trictures and properties of the polymers are characterized and evaluated by IR, NMR,TGA, UV, photoluminescence (PL), and electroluminescence (EL) analyses. All the polymers possess high thermal stabilityand emit strong blue ligh upon photoexcitation. The intensity of the emitted light is greater than that of poly(1-phenyl-1-octyne), a well-known highly luminescent disubstituted polyacetylene. Little aggregation-induced red shift in the PL wasobserved in the thin films of the polymers. By constructing a multi-layer EL device, high EL quantum yield (0.18%) has beenachieved in 2, which are the best results for substituted polyacetylenes attainable so far.     

Effect of a perfluorocyclopentene core unit on the structures and photoluminescence of fluorene- and anthracene-based compounds

A novel series of blue luminescent compounds, in which three identical functional groups, such as fluorene, anthracene, and spiro-bifluorene, are linked distortedly around a perfluorocyclopentene core, have been synthesized and characterized. The introduction of a perfluorocyclopentene linkage into the molecular framework leads to an enhancement of the photoluminescence (PL) efficiency and thermal stability. All compounds exhibit intense blue photoluminescence, which has been attributed to fluorene- or anthracene-based π→π* transitions. The maximum emission wavelengths of all compounds at room temperature are in the region of 420-480 nm, with higher PL quantum efficiencies than in 9,10-diphenylanthracene. The electroluminescent (EL) properties of compound 4, 1,2-bis(9,9′-spirobifluoren-2-yl)-3,3,4,4,5,5-hexafluorocyclopentene, were investigated. A multilayer EL device with the configuration of ITO/2TNATA(60 nm)/NPB(20 nm)/ADN:2%-compound-4(35 nm)/Alq₃(20 nm)/LiF(2 nm)/Al has been successfully fabricated.     

Light-emitting conjugated molecule containing 1,3,4-oxadiazole, carbazole and naphthalene units

A novel pi-conjugated small molecule VNCO, 2,5-bis{3'-[3'-vinyl-9'-(alpha-naphthyl)carbazolyl]phenyl}-1,3,4-oxadiazole, containing hole-transporting carbazole moieties, electron-injecting 1,3,4-oxadiazole moieties and chromophore naphthalene was designed and synthesized by Wittig reaction of 2,5-bis(3-tolylene-triphenylphosphonium bromide)-1,3,4-oxadiazole and 3-formyl-9-(alpha-naphthyl)carbazole. The UV-vis absorption, fluorescence excitation and emission spectra have been obtained in solution for VNCO. The photoluminescence (PL) of VNCO were examined in different solvents and the luminescence quantum yield was 0.746 in chloroform. It emitted blue and blue-green light, with the band gap of 3.30 eV estimated from the onset absorption. In addition, the light-emitting can be quenched by both electron donor (N,N-dimethylaniline) and electron acceptor (dimethylterephalate). Furthermore, the molecular interactions of VNCO with fullerene (C60) or carbon nanotubes (CNTs) were also carefully investigated.     

吡啶-芴类电荧光聚合物的光谱特性

用Suzuiki聚合反应将二溴代吡啶 (2 ,5 、2 ,6 、3,5 取代 )与芴共聚 ,合成了不同主链结构的吡啶 芴共聚物 .研究结果表明 ,将吡啶基引人聚芴主链可以调节共聚物的发光颜色 .间位吡啶基引入聚芴主链 ,使聚合物的能级加宽 ,PL、EL光谱发生蓝移 ;对位吡啶基则使光谱红移 .间位吡啶基 (3,5 Py、2 ,6 Py)引入聚芴主链 ,可提高聚合物的色纯度 .共聚物中 3,5 Py含量为 4 0mol%时 ,可得到较纯的蓝光 .     

Thermotropic liquid crystalline polymers containing five-membered heterocyclic groups IX. Synthesis and optical properties of liquid crystalline semi-rigid polyesters composed of a quinquephenyl analogue containing 1,3,4-thiadiazole and aliphatic chains

Novel semi-rigid polyesters containing a quinquephenyl analogue containing 1,3,4-thiadiazole and a central 1,3-phenylene unit in the main chain were synthesized by high temperature solution polycondensation of a dimethyl ester derivative of 1,3-bis(5-phenyl-1,3,4-thiadiazol-2-yl)benzene with an aliphatic (octa-, deca- and dodecamethylene) diol. The proposed structures were confirmed using FTIR and ¹H NMR spectroscopies, and elemental analyses; their liquid crystalline and photoluminescent (PL) properties were examined by means of differential scanning calorimetry, optical texture observations using polarizing microscopy, powder X-ray diffraction, and UV-vis and PL spectra measurements. These measurements showed that the polymers not only show a monotropic solid smectic or disordered crystal phase, but also PL properties with blue emission in HFIP solutions and in the solid phase, Stokes shifts of 116.5–119?nm being observed.     

Synthesis and characterization of bipolar copolymers containing oxadiazole and carbazole pendant groups and their application to electroluminescent devices

A series of random copolymers POC10{Poly(2,5‐bis[(5‐decyloxy‐phenyl)‐1,3,4‐oxadiazole]styrene)}‐co‐Poly(N‐vinylcarbazole) (PVK) with different nvk content were synthesized through common radical polymerization and were incorporated into light emitting diodes as emitting layers. The structures and properties of the copolymers were characterized and evaluated by GPC, TGA, DSC, UV, PL, CV, and EL analyses. All the polymers enjoy high thermal stability. Cyclic voltammetry revealed that, with the incorporation of N‐vinylcarbazole to the copolymer, these copolymers had high‐lying HOMO energy values, which facilitated hole injection. PL peaks in the film show blue‐shift compared with those in solutions and fluorescent quantum efficiency decreased with the nvk content increasing, which supported the efficient energy transfer from nvk units to the oxadiazole units. Single‐layer LEDs with the configuration of ITO/PEDOT/PC10‐nvk/Mg:Ag/Ag were fabricated, which emit a blue light around 440 and 490 nm with a maximum brightness of 675.3 cd/m² and luminous efficiency of 0.108 cd/A. Moreover, we fabricated electrophosphorescent device from bipolar transport copolymer PC10‐nvk4 as host material and an orange‐light‐emitting iridium phosphor IrMDPP as guest. The maximum luminous efficiency of 0.548 cd/A was obtained. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5452–5460, 2008     

Optimization of high-performance blue organic light-emitting diodes containing tetraphenylsilane molecular glass materials

Molecular glass material (4-(5-(4-(diphenylamino)phenyl)-2-oxadiazolyl)phenyl)triphenylsilane (Ph(3)Si(PhTPAOXD)) was used as the blue light-emitting material in the fabrication of high-performance organic light-emitting diodes (OLEDs). In the optimization of performance, five types of OLEDs were constructed from Ph(3)Si(PhTPAOXD): device I, ITO/NPB/Ph(3)Si(PhTPAOXD)/Alq(3)/Mg:Ag, where NPB and Alq(3) are 1,4-bis(1-naphylphenylamino)biphenyl and tris(8-hydroxyquinoline)aluminum, respectively; device II, ITO/NPB/Ph(3)Si(PhTPAOXD)/TPBI/Mg:Ag, where TPBI is 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene; device III, ITO/Ph(2)Si(Ph(NPA)(2))(2)/Ph(3)Si(PhTPAOXD)/TPBI/Mg:Ag, where Ph(2)Si(Ph(NPA)(2))(2) is bis(3,5-bis(1-naphylphenylamino)phenyl)-diphenylsilane, a newly synthesized tetraphenylsilane-containing triarylamine as hole-transporting material; device IV, ITO/Ph(2)Si(Ph(NPA)(2))(2)/NPB/Ph(3)Si(PhTPAOXD)/TPBI/Mg:Ag; device V, ITO/CuPc/NPB /Ph(3)Si(PhTPAOXD)/Alq(3)/LiF/Al, where CuPc is Cu(II) phthalocyanine. Device performances, including blue color purity, electroluminescence (EL) intensity, current density, and efficiency, vary drastically by changing the device thickness (100-600 A of the light-emitting layer) and materials for hole-transporting layer (NPB and/or Ph(2)Si(Ph(NPA)(2))(2)) or electron-transporting material (Alq(3) or TPBI). One of the superior OLEDs is device IV, showing maximum EL near 19 000 cd/m(2) with relatively low current density of 674 mA/cm(2) (or near 3000 cd/m(2) at 100 mA/cm(2)) and high external quantum efficiency of 2.4% (1.1 lm/W or 3.1 cd/A). The device possesses good blue color purity with EL emission maximum (lambda(max)(EL)) at 460 nm, corresponding to (0.16, 0.18) of blue color chromaticity on CIE coordinates. In addition, the device is reasonably stable and sustains heating over 100 degrees C with no loss of luminance on the basis of the annealing data for device V. Formation of the exciplex at the interface of NPB and Ph(3)Si(PhTPAOXD) layers is verified by EL and photoluminescence (PL) spectra studies on the devices with a combination of different charge transporting materials. The EL due to the exciplex (lambda(max)(EL) at 490-510 nm) can be properly avoided by using a 200 A layer of Ph(3)Si(PhTPAOXD) in device I, which limits the charge-recombination zone away from the interface area.     

CHARACTERIZATION AND LUMINESCENCE PROPERTIES OF THE DYE-DOPED POLYMER LANGMUIR-BLODGETT FILMS*

1,1,4,4-Tetraphenyl-1,3-butadiene (TPB) was successfully introduced into the polymer multilayerfilms by means of Langmuir-Blodgett (LB) technique. Results of UV-VIS spectra and X-ray diffractionshowed that the uniform films had a layer structure similar to the superlattice of organic multiple quantumwells. The electroluminescence (EL) devices fabricated from the doped polymer LB films emitted blue light.Compared with the casting films, the photoluminescence (PL) and EL spectra showed that the exciton energyshifts to higher and the half-width of the emission peak becomes narrower due to exciton confinement effect.     

新型双极有机小分子化合物及其Al3+配合物的合成与发光

合成了一种新的具有“双极”(bipolar)性质的有机小分子蓝色发光材料2-(5-(4-(二苯胺基)苯基)-1,3,4-噁二唑-2-)苯酚［2(5-(4-(diphenylamino)phenyl)-1,3,4-oxadiazol-2-yl)phenol, HPOT］, 并以HPOT为配体, 与铝离子配位, 合成了三(2-(5-(4-(二苯胺基)苯基) 1,3,4-噁二唑-2-)苯酚)合铝［tri(2-(5-(4-(diphenylamino)phenyl)-1,3,4-oxadiazol-2-yl)phenonate)aluminum, AlPOT］配合物. 用 1 H NMR、 HRMS和元素分析进行了表征, 并测定了两种化合物的光致发光性质和热稳定性. 结果表明: 两种新化合物的热稳定性好, 光致发光性能优良, 是制作有机电致发光器件的候选材料.     

Blue luminescence induced by confinement in self-assembled films

The fabrication and characterization by means of photoluminescence (PL), UV-vis absorption, electro-luminescence (EL) and X-ray reflectivity of multilayer heterostructures consisting of alternate layers of conjugated and non-conjugated polymers have been studied. The heterostructures are prepared by the layer-by-layer self-assembly technique, using two types of polyelectrolytes. The first are precursors of conjugated polymers such as poly(phenylenevinylene) (PPV) and other poly(arylenevinylene) polymers, and the second are non-conjugated polymers such as poly(styrene-4-sulfonate) (SPS), polyacrylic acid (PAA) and poly(allylamine hydrochloride) (PAH). The heterostructures consist of a repeated sequence of bilayers (layer pair) or multilayers, where the conjugated polymer is formed by heat treatment under vacuum. The thickness of each bilayer or multilayer was controlled by changing the non-conjugated polymer layer. Most importantly, we have found that the PL and EL spectral emissions can be ‘tuned’ by a proper ‘design’ of the heterostructure. Particularly, heterostructures in which the bilayer thickness is rather small and the electroluminescent layers are practically in contact show a blue shift upon decreasing the thickness of the assembly for ultrathin assemblies. In contrast, for assemblies where the electroluminescent layers are well separated by one or several non-conjugated layers (polyelectrolyte spacers), the emission is in the blue and independent of the assembly thickness (number of bilayers). We interpret the results as being due to confinement effects. Using this assembly technique, we were able to fabricate light emitting diodes (LEDs) which emit in the blue region.     

Phenothiazine‐S,S‐dioxide‐ and fluorene‐based light‐emitting polymers: Introduction of e−‐deficient S,S‐dioxide into e−‐rich phenothiazine

A novel series of poly(10‐hexyl‐phenothiazine‐S,S‐dioxide‐3,7‐diyl) and poly(9,9′‐dioctyl‐fluorene‐2,7‐diyl‐alt‐10‐hexyl‐3,7‐phenothiazine‐S,S‐dioxide) (PFPTZ‐SS) compounds were synthesized through Ni(0)‐mediated Yamamoto polymerization and Pd(II)‐catalyzed Suzuki polymerization. The synthesized polymers were characterized by ¹H NMR spectroscopy and elemental analysis and showed higher glass transition temperatures than that of pristine polyfluorene. In terms of photoluminescence (PL), the PFPTZ‐SS compounds were highly fluorescent with bright blue emissions in the solid state. Light‐emitting devices were fabricated with these polymers in an indium tin oxide/poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate)/polymer/Ca/Al configuration. The electroluminescence (EL) of the copolymers differed from the PL characteristics: the EL device exhibited a redshifted greenish‐blue emission in contrast to the blue emission observed in the PL. Additionally, this unique phenothiazine‐S,S‐dioxide property, triggered by the introduction of an electron‐deficient SO₂ unit into the electron‐rich phenothiazine, gave rise to improvements in the brightness, maximum luminescence intensity, and quantum efficiency of the EL devices fabricated with PFPTZ‐SS. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1236–1246, 2007