Structures, electronic states, photoluminescence, and carrier transport properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles

The excellent electroluminescent (EL) properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles, 1-methyl-1,2,3,4,5-pentaphenylsilole (MPPS), and 1,1,2,3,4,5-hexaphenylsilole (HPS) have been found. Despite some studies devoted to these materials, very little is known about the real origin of their unique EL properties. Therefore, we investigated the structures, photoluminescence (PL), and charge carrier transport properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles as well as the effect of substituents on these characteristics. The single crystals of the three siloles involving 1,1-dimethyl-2,3,4,5-tetraphenylsilole (DMTPS), MPPS, and HPS were grown and their crystal structures were determined by X-ray diffraction. Three siloles have nonplanar molecular structures. The substituents at 1,1-positions enhance the steric hindrance and have predominant influence on the twisted degree of phenyl groups at ring carbons. This nonplanar structure reduces the intermolecular interaction and the likelihood of excimer formation, and increases PL efficiency in the solid state. The silole films show high fluorescence quantum yields (75-85%), whereas their dilute solutions exhibit a faint emission. The electronic structures of the three siloles were investigated using quantum chemical calculations. The highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) are mainly localized on the silole ring and two phenyl groups at 2,5-positions in all cases, while the LUMOs have a significant orbital density at two exocyclic Si-C bonds. The extremely theoretical studies of luminescent properties were carried out. We calculated the nonradiative decay rate of the first excited state as well as the radiative one. It is found that the faint emission of DMTPS in solutions mainly results from the huge nonradiative decay rate. In solid states, molecular packing can remarkably restrict the intramolecular rotation of the peripheral side phenyl ring, which has a large contribution to the nonradiative transition process. This explains why the 1,1-disubstituted 2,3,4,5-tetraphenylsiloles in the thin films exhibit high fluorescence quantum yields. The charge carrier mobilities of the MPPS and HPS films were measured using a transient EL technique. We obtained a mobility of 2.1 x 10(-)(6) cm(2)/V.s in the MPPS film at an electric field of 1.2 x 10(6) V/cm. This mobility is comparable to that of Alq(3), which is one of the most extensively used electron transport materials in organic light-emitting diodes (LEDs), at the same electric field. The electron mobility of the HPS film is about approximately 1.5 times higher than that of the MPPS film. To the best of our knowledge, this kind of material is one of the most excellent emissive materials that possess both high charge carrier mobility and high PL efficiency in the solid states simultaneously. The excellent EL performances of MPPS and HPS are presumably ascribed to these characteristics.     

An organic electroluminescent device with a molecularly doped polymer hole transport layer

Electroluminescent(EL) devices have been fabricated using four different polymers with different glass transition temperatures (T_g) dispersed with N,N′-bis-(3-methylphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (TPD) as a hole transport layer and tris(8-hydroxyquinoline) aluminum (Alq₃) as an emitting layer. It was found that the higher the T_g of the polymer, the longer the lifetime of the device. From observations of TPD-doped polymer films with optical microscope and atomic force microscope, dispersing TPD in the polymers was found to suppress the crystallization that causes the roughness of the film surface. It was also observed that the higher the T_g of the host polymers, the more difficult TPD crystallization was. The property of the EL device with polyethersulfone (PES) dispersed with TPD was also investigated. The lifetime of EL device with the TPD doped PES film was improved more than five times at a current density below 10 mA/cm² compared with the device with a conventional TPD hole transport layer. © 1997 John Wiley & Sons, Ltd.     

Competition between the charge transfer state and the singlet states of donor or acceptor limiting the efficiency in polymer:fullerene solar cells

We study the appearance and energy of the charge transfer (CT) state using measurements of electroluminescence (EL) and photoluminescence (PL) in blend films of high-performance polymers with fullerene acceptors. EL spectroscopy provides a direct probe of the energy of the interfacial states without the need to rely on the LUMO and HOMO energies as estimated in pristine materials. For each polymer, we use different fullerenes with varying LUMO levels as electron acceptors, in order to vary the energy of the CT state relative to the blend with [6,6]-phenyl C61-butyric acid methyl ester (PCBM). As the energy of the CT state emission approaches the absorption onset of the blend component with the smaller optical bandgap, E(opt,min) ≡ min{E(opt,donor); E(opt,acceptor)}, we observe a transition in the EL spectrum from CT emission to singlet emission from the component with the smaller bandgap. The appearance of component singlet emission coincides with reduced photocurrent and fill factor. We conclude that the open circuit voltage V(OC) is limited by the smaller bandgap of the two blend components. From the losses of the studied materials, we derive an empirical limit for the open circuit voltage: V(OC) ? E(opt,min)/e - (0.66 ± 0.08)eV.     

分子构型对有机半导体分子TPD,DDB和NPB激射性能的影响

N,N′-二苯基-N,N′-二（3-甲苯基）-1,1′-联苯-4,4′-二胺（TPD）分子已证明能够在掺杂和非掺杂平面波导结构中产生受激发射,然而对于该分子激射特性的机理却很模糊.为了得到其激射特性的微观解释,我们通过实验和量化理论研究TPD分子的吸收、光致发光、受激发射以及与TPD分子结构类似的两个分子：1,4-二（二苯胺基）联苯（DDB）和N,N′-二苯基-N,N′-二（1-萘基）-1,1′-联苯-4,4′-二胺（NPB）.我们发现,DDB分子具有与TPD分子相似的自发辐射放大（ASE）特性,然而NPB分子却没有ASE特性,尽管其斯托克斯位移较大,约0.754eV.量子化学计算分析中,我们利用密度泛函理论（DFT）和弗朗克-康登（Franck-Condon）原理研究分子在电子基态和激发态的分子构型以及电子基态的振动能级.理论分析表明,对于TPD和DDB分子,一些苯环中的较强高频拉伸模式（1199～1664cm-1）对PL谱中的第一振动带（0-1跃迁）有显著贡献,该振动带有利于形成激光的四能级系统.而对于NPB分子,相对大的萘基基团取代了TPD和DDB分子外围的甲基与苯环,会产生一些较强的分子低频振动模式（11～689cm-1）,这些低频振动模式则会破坏激光四能级系统.研究结果有助于深刻理解有机分子的激射特性,为新型激射材料的设计和应用提供了理论基础.     

Supramolecular structures and assembly and luminescent properties of quinacridone derivatives

The synthesis and single-crystal X-ray structures of two quinacridone derivatives, N,N'-di(n-butyl)quinacridone (1) and N,N'-di(n-butyl)-1,3,8,10-tetramethylquinacridone (2), are reported, and the 1H NMR, absorption, photoluminescent (PL), and electroluminescent (EL) characteristics are presented. Both these crystal structures are characterized by intermolecular pi...pi and hydrogen bonding interactions. The intermolecular pi...pi interactions lead to the formation of molecular columns in the solids of 1 and 2, and the interplanar contact distances between two adjacent molecules are 3.48 and 3.55 angstroms, respectively. Crystals of 1 display shorter intermolecular pi...pi contacts and higher density than 2. These results suggest that tighter intermolecular interactions exist in 1. The 1H NMR, absorption, and PL spectra of 1 and 2 in solutions exhibit concentration-dependent properties. The PL quantum yields of 1 in solutions decrease more quickly with the increase of concentration compared to that of 2 in solutions. For solid thin films of Alq3:1 (Alq3 = tris(8-hydroxyquinolinato)aluminum), emission intensities dramatically decrease and obvious red shifts are observed when the dopant concentration is above 4.2%, while for films of Alq3:2, a similar phenomenon occurs when the concentration is above 6.7%. EL devices with Alq3:1 as emitting layer only show high efficiencies (20.3-14.5 cd/A) within the narrow dopant concentration range of 0.5-1.0%. In contrast, high efficiencies (21.5-12.0 cd/A) are achieved for a wider dopant concentration range of 0.5-5.0% when Alq3:2 films are employed as emitting layer. The different PL and EL concentration-dependent properties of the solid thin films Alq3:1 and Alq3:2 are attributed to their different molecular packing characteristics in the solid state.     

Electroluminescence from Exciplex on the Interface Between TPD and La（PMIP）3（Bipy）

The bilayer organic light-emitting diode(OLED) with a blue fluorescent lanthanum complex, tris(1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone)-(2,2′-dipyridyl) lanthanum [La(PMIP)3(Bipy)], as a light emitting material and N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine(TPD) as a hole transporting material emits bright green light instead of blue light. The data of the absorption, the photoluminescence(PL) and the photoluminescence excitation(PLE) spectra of TPD, La(PMIP)3(Bipy) and the mixture of TPD and La(PMIP)3(Bipy)(molar ratio 1∶1) prove that the electroluminescent emission originates from the exciplex on the interface between TPD and La(PMIP)3(Bipy). By improving device configuration with tris(8-hydroxyquinoline) aluminum(ALQ) as an electron transporting material, a maximum luminance of 800 cd/m2 was obtained.     

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.     

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.     

Application of chelate phosphine oxide ligand in EuIII complex with mezzo triplet energy level, highly efficient photoluminescent, and electroluminescent performances

The chelate phosphine oxide ligand bis(2-(diphenylphosphino)phenyl) ether oxide (DPEPO) was used as a unit neutral ligand to prepare the complex Eu(TTA)(3)(DPEPO) 1 (TTA = 2-thenoyltrifluoroacetonate). Compound 1 has a photoluminescence (PL) quantum yield of 55.3%, which is more than the twice of the PL quantum yield of Eu(TTA)(3)(TPPO)(2) (TPPO = triphenylphosphine oxide). Investigation indicated that DPEPO in 1 has the mezzo first triplet excited energy level (T(1)) between the first singlet excited energy level (S(1)) and T(1) of TTA, which may support one more additional energy transfer routines from the T(1) energy level of DPEPO to that of TTA, and consequently results in the improvement of energy transfer in the Eu(III) complex. DPEPO forms a complex with a more rigid and compact structure that can improve energy transfer between ligands and the center Eu(III) ion, support the higher saturation level by the coordinating ability of the oxygen atom in the ether moiety, and consequently enhance the PL intensity and efficiency of the corresponding Eu(III) complex. The multilayered electroluminescent (EL) device of 1 used as the red dopant exhibited an impressive brightness of 632 cd m(-2) at 25 V. The device had the excellent voltage-independent spectral stability with an emission peak at 615 nm. To the best of our knowledge, this luminescence is the brightest emission among Eu complexes with phosphine oxide ligands. The maximum external quantum yield (eta(ext)) of 2.89% and the maximum current and power efficiency of 4.58 cd A(-1) and 2.05 lm W(-1) were achieved at a low turn-on voltage of 7 V and current density of 0.021 mA cm(-2). These properties demonstrate that the chelate phosphine oxides ligand DPEPO can not only be favorable to form the rigid and compact complex structure and increase the efficiency of devices, but also reduce the ability of the formation of exciplex. DPEPO shows much better performance compared with the ordinary phosphine oxide ligand triphenylphosphine oxide.     

Red Electroluminescence and Photoluminescence from Novel Binuclear Europium Complex with Squaric Acid Ligand

Organic electroluminescent devices (OELDs) have attracted much attention for several years because of their potential application in large area, multi-colored flat panel displays1-5. The green organic EL display using Alq3 as emitter was commercialized in 19976. However, red-emitting OELD with excellent properties has not been well developed. In order to realize practical full-color OELDs, it is considered very important to develop red and blue emitting materials with excellent propert…     

可溶性8-羟基喹啉铝衍生物电致发光材料的合成及性质

本文设计合成了五种可溶性8-羟基喹啉合铝的衍生物，结构经红外、核磁共振及元素分析表征，并对它们的光致发光以及分子结构与发光性能的关系进行了研究。     

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.     

Temperature-dependent photoluminescence of organic light-emitting materials: Types and characteristics of excitons involved in the emitting process

Based on experimental measurement and theoretical analysis, the temperature dependence of the photoluminescence (PL) of amorphous thin films of tris-(8-hydroxyquinoline) aluminum (Alq) and 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) has been studied. It is proposed that three types of excitons with different charge separations are involved in the steady state PL process. It is found that all three types of excitons participate in the PL process of Alq, whereas, only the first two types of radiative excitons dominate the PL process of DCJTB in the temperature range covered by the present work. The blue shift of the DCJTB PL spectra with increasing temperature has been observed and analyzed. It is suggested that the temperature-dependence of PL could be used to evaluate the radiative and conductive characteristics of organic emitters and to distinguish whether a given material would tend to be of molecular or semiconductor properties.     

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.     

Luminescence of monolayer thin films of the fully conjugated rigid‐rod polymer poly(p‐phenylenebenzobisthiazole)

Poly(p‐phenylenebenzobisthiazole) (PBT) is a heterocyclic, aromatic rigid‐rod polymer with a fully conjugated backbone and excellent dimensional, thermo‐oxidative, and solvent stabilities. A PBT polymer with an intrinsic viscosity of 18.0 dL/g was dissolved in methanesulfonic acid or Lewis acid. The PBT solution was spin‐coated and doctor‐bladed for freestanding films or onto an indium tin oxide (ITO) substrate. The acid was removed via coagulation. Scanning electron microscopy determined that the resultant film thicknesses were about 340 and 60 nm for PBT freestanding films and films on the ITO substrate, respectively. X‐ray scattering demonstrated that the freestanding films were in‐plane isotropic without long‐range order. The freestanding films were excited with a He‐Cd laser at 325 nm for photoluminescence (PL) response. PL spectra showed a distinct intensity maximum at 580 nm, regardless of the film‐forming conditions. After the films cooled to 67 K, the PL maximum shifted to 566 nm with enhanced intensity. Aluminum was evaporated onto the monolayer PBT thin film on the ITO substrate as an electron injector for electroluminescence (EL) response. Diodic electric behavior was observed for all monolayer PBT EL devices for the first time. A threshold voltage as low as 4 V was achieved for the monolayer EL devices. In addition, PBT EL spectra were tunable, with a maximum intensity at 570 nm at a bias voltage of 4.5 V changing to 496 nm at 7.5 V (i.e., a blueshift) with greatly increased intensity. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1760–1767, 2002     

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.     

Coumarin‐containing poly(fluorenediylvinylene)s: Synthesis,photophysics, and electroluminescence

Two new poly(fluorenediylvinylene)s (CV and CF) with coumarin side chains were synthesized via Heck coupling. The coumarin segments were attached to the C‐9 of fluorene through alkyl spacers. The polymers were soluble in common organic solvents such as tetrahydrofuran (THF), chloroform, dichloromethane, and toluene. The photoluminescence (PL), electroluminescence (EL), and electrochemical behavior of these polymers were studied. CV and CF thin films exhibited broad‐band, bluish‐green and orange PL emissions, with maxima at 475 and 585 nm, respectively. These PL maxima were redshifted in comparison with those measured in THF solutions. Aggregate formation played an important role in the solid state. The aggregation was more pronounced in CF thin films than CV thin films. Both polymers oxidized and reduced irreversibly. Light‐emitting devices (LEDs) with indium tin oxide hole‐injecting and aluminum electron‐injecting electrodes were prepared and studied. The LEDs made of CV emitted green light, and the LEDs made of CF exhibited an orange EL emissions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5750–5762, 2006     

Excited state properties of neutral, anionic and cationic 1,1-disubstituted 2,3,4,5-tetraphenylsiloles: A quantum chemical characterization

Structure, electronic states, photoluminescence, and carries transport properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles for light-emitting diodes were investigated experimentally [G. Yu, et al, J. Am. Chem. Soc. 2005, 127, 6335], and the excellent electroluminescent (EL) properties of them have been found. In this paper, excited state properties of neutral, anionic and cationic 1,1-disubstituted 2,3,4,5-tetraphenylsiloles are studied with quantum chemistry method as well as the 3D real space analysis methods. The transition densities of neutral, anionic and cationic 1,1-disubstituted 2,3,4,5-tetraphenylsiloles show that the orientations and strengths of dipole moments the neutral, anionic and cationic ones are significantly different, where the neutral 1,1-disubstituted 2,3,4,5-tetraphenylsiloles show the Frenkel character; while the anionic and cationic 1,1-disubstituted 2,3,4,5-tetraphenylsiloles show the plasmon character. The charge difference densities of neutral, anionic and cationic 1,1-disubstituted 2,3,4,5-tetraphenylsiloles reveal the important diversity of the orientations and the results of intramolecular charge transfer (ICT). The theoretical results also reveal the contribution of the substituents at the 1,1-position to the neutral and charged excited state properties of 2,3,4,5-tetraphenylsiloles. The calculated results are consistent with the experimental results, and further provide the insight of understanding to the excited state properties of neutral, anionic and cationic 1,1-disubstituted 2,3,4,5-tetraphenylsiloles.     

中位四(1-苯基吡唑-4-基)卟啉掺杂空穴传输材料的红色有机电致发光器件(英文)

使用中位-四(1-苯基吡唑-4-基)卟啉(TPPyPH2)掺杂空穴传输材料N,N′-二苯基-N,N′-双(4-甲苯基)-1,1′-二苯基-4,4′-二胺(TPD)制备了红色有机电致发光器件.因为TPD的发射光谱与TPPyPH2的吸收光谱具有更大的光谱重叠,为了得到更为有效的从主体材料TPD向红光染料TPPyPH2的能量传递,我们使用TPD代替传统的8-羟基喹啉铝(Alq3)作为主体发光材料.器件在680nm处具有纯的红光发射峰;通过使用Alq3电子传输层以及使用Alq3共掺杂发光层的方法,使器件的发光性能得到了改善,结构为ITO/Alq3+TPPyPH2+TPD(50nm)/Alq3(30nm)/Al的器件的最大发光亮度为177cd/m2.     

铕配合物共掺杂电致发光器件效率滚降的延缓

将Alq₃[tris(8-hydroxyquinoline)aluminium]和Eu(TTA)₃phen(TTA=thenoyltrifluoroacetone,phen=1,10-phenanthroline)共掺杂进入主体材料CBP(4,4’-N,N’-dicarbazole-biphenyl)中,我们制作并研究了一系列电致发光器件。经过优化Alq₃的掺杂浓度,在不改变色纯度的情况下,器件的效率滚降被大幅降低并获得了近乎加倍的最大亮度。发光层中的Alq₃分子不仅促进了电子的注入和传输,还延缓了空穴的传输。借助电致发光光谱,我们证实Alq₃分子作为阶梯加速空穴从CBP分子到Eu(TTA)₃phen分子的迁移,从而促进了电子和空穴在Eu(TTA)₃phen分子上的平衡。因此,我们认为器件的效率滚降受到抑制的原因有两点：一是复合区间的加宽,二是Eu(TTA)₃phen分子上空穴和电子的分布更加平衡。