Preparation and Characterization of 2,2-bis[4-(3-Aminophenoxy)phenyl]propane/4,4′-Oxydianiline/4,4′-Oxydiphthalic Anhydride (3-BAPOPP/44ODA/ODPA) Polyimide Films with Various Co-monomer Ratios

A new diamine monomer 2,2-bis[4-(3-aminophenoxy)phenyl]propane (3-BAPOPP) was synthesized through two steps and its melting point was determined by differential scanning calorimetry (DSC). It was then copolymerized with 4,4′-oxydianiline (44ODA) and 4,4′-oxydiphthalic anhydride (ODPA) to obtain a series of aromatic polyimide(3-BAPOPP/44ODA/ODPA-PI) films. Fourier transform infrared (FT-IR) was used to characterize the structures of the monomer and the polyimide films. Water absorption, ultraviolet-visible (UV-Vis) spectroscopy, contact angle, DSC, and thermo-gravimetric analysis (TGA) were used to characterize the properties of 3-BAPOPP/44ODA/ODPA-P films. The results showed that the PI films had low water absorption in the range of 1.5%～1.9%, low surface energy in the range of 43.3 ～43.5 mJ/m², glass transition temperature (T_g) in the range of 192.5°C～226.1°C, and dielectric constant in the range of 2.79～3.02 at 1 MHz. The films also exhibited good thermal properties and good optical properties, with the ultra violet cut-off wavelength being in the range of 346～364 nm.     

Preparation and Characterization of Novel Polyimides with Hydroxyl Groups

3,3′-diamino-4,4′-dihydroxybiphenyl (DADHBP) was synthesized and its chemical structure was confirmed by Fourier transform infrared (FT-IR) spectroscopy, ¹H-nuclear magnetic resonance (¹H-NMR), and differential scanning calorimetry (DSC). Then six poly(amic acid) (PAA) solutions were prepared by copolymerization of DADHBP, oxydiphthalicanhydride (ODPA), and 2,2-bis [4-(4-aminophenoxy)phenyl] propane (BAPOPP) in N,N-dimethylacetamide (DMAC) in different mole ratios. The polyimide (PI) films were obtained through thermal imidazation reactions of the thin layers of the above-mentioned precursor solutions. Chemical structures of all PI films were demonstrated by FT-IR. Thermal stabilities and decomposition behaviors of the PI films were tested by DSC and thermogravimetric analysis (TGA). Thermal measurements indicate that the polymers have high thermal stability and produce high char yields. The properties of the PI films were further studied by ultraviolet–visible spectroscopy, water absorption, surface energy, and mechanical measurements. Thermal analysis showed glass transition temperatures between 205.9°C and 276.7°C. Decomposition temperatures were higher than 360.2°C, with 10% weight losses in the range of 448.6°C～517.8°C. The prepared PI films also exhibited good UV absorption, low water absorption (<2%), low surface energy (<44.28 mJ/m²), and good mechanical properties.     

Solution-processed white organic light-emitting diodes with mixed-host structures

Efficient white light-emitting diodes (WOLEDs) were fabricated with a solution-processed single emission layer composed of a molecular and polymeric material mixed-host (MH). The main host used was a blue-emitting molecular material of 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi) and the assisting host used was a hole-transport-type polymer of poly(9-vinylcarbazole) (PVK). By co-doping 4,4′-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl and 5,6,11,12-tetraphenylnaphacene into the MH, the performances of the fabricated devices made with different mixing ratio of host materials were investigated, and were to depend on the mixing ratios. Under the optimal PVK:DPVBi ratio (3:7), we achieved a maximum luminance of 14 110 cd/m² and a maximum current efficiency of 9.5 cd/A. These improvements were attributed to the MH structure, which effectively improved the thermal stability of spin-coated film and enhanced the hole-injection/transporting properties of WOLEDs.     

High Optical Transparency and Low Dielectric Constant Polyimides Containing Trifluoromethyl and Cyclohexane Groups

A series of novel polyimides (PIs) were polymerized from 4,4′-(cyclohexane-1,4-diylbis (oxy))bis(3-(trifluoromethyl)aniline) (1) and 1,4-bis((4-amino-2-(trifluoromethyl) phenoxy)methyl)cyclohexane (2), with two aromatic tetracarboxylic dianhydrides using the typical one-step method. The inherent viscosity of these resulting PIs were in the range of 0.53–0.91 dl/g in N,N-dimethylacetamide (DMAc) at 30°C. They were readily soluble in numerous solvents, such as N-methyl-2-pyrrolidone (NMP), DMAc, N,N-dimethylformamide (DMF), meta-cresol (m-Cresol), and dimethylsulfoxide (DMSO). The PI films showed high optical transparency and were colorless with an ultraviolet-visible absorption cut-off wavelength around 330 nm, and a low dielectric constants of 2.49–2.93 at 1 MHz. The PIs also showed good thermal properties. Their glass-transition temperatures (T _g) were higher than 337°C, and the temperatures of 10% weight loss in air and nitrogen were higher than 412°C and 417°C. Furthermore, the PI films possessed good mechanical properties with tensile strengths of 54–71 MPa, elongations at break of 11.6%–17.3% and low moisture absorption (<1.34%). Due to their properties, these PIs could be considered as materials for photoelectric and micro-electronic applications.     

Molecular order and dynamic mechanical behavior of polyurethanes based on liquid crystalline diol

Synthesis of the liquid crystalline (LC) diol 6,6′-[ethylenebis(l,4-phenylene-oxy)]-dihexanol (I) is described. The structure of polyurethanes prepared from diol I and 4,4′-methylenedi(phenyl isocyanate) (MDI), 4,4′-methylenedi(cyclohexyl isocyanate) (HMDI), or 2(4)-methyl-l,3-phenylene diisocyanate (TDI) at 1:1 molar ratios of isocyanate and hydroxy groups is studied by dynamic mechanical spectroscopy, differential scanning calorimetry (DSC), polarizing microscopy, and x-ray scattering. The polymer prepared from HMDI and the diol (I/HMDI) shows, on cooling, thermal behavior typical of amorphous polymers. A frequency-temperature superposition could be applied to the mechanical data, and the horizontal shift factor satisfied the Williams-Landel-Ferry (WLF) equation. A more-complex thermal behavior was found for I/HMDI polymer during subsequent heating; above 70°C, the formation of an ordered structure takes place, and this structure melts at about 120°C. Complex thermal behavior is exhibited by I/TDI polymer. On cooling its melt, the polymer forms a nematic phase at about 80°C, which freezes into the LC glassy state. On heating, the mesophase melts, and. subsequently, a better-ordered smectic phase is formed at 95°C, which melts at 120°C. This structure buildup is accompanied by a rapid increase in storage modulus G′, and the sample shows thermorheologically complex mechanical behavior. The polymer formed from the diol and MDI (I/MDI) exhibits a most-complex thermal behavior. On cooling and heating, four transitions can be detected in its thermal mechanical behavior, and the structure of the polymer is strongly dependent on its thermal history.     

Synthesis and luminescent properties of bithiazole derivatives

New blue photoluminescent materials 4,4^′-bis(1-naphthyl)-2,2^′-bithiazole (BNBT) and 4,4^′-bis(4-biphenyl)-2,2^′-bithiazole (BPBT) were synthesized by the facile reaction of 2-bromoacetoaromatic compound with dithioxamide. The resulting BNBT and BPBT having thiazole moiety were characterized by NMR, infrared (IR), UV/visible absorption and are well vacuum deposited for thin films. The BNBT and BPBT show blue photoluminescent (PL) spectra at 437 and 432 nm, respectively, and typical rectifying diode characteristics in ITO/BNBT or BPBT/Al device. The BNBT and BPBT are thermally stable up to 330°C and 360°C, respectively, under N₂.     

Synthesis and Properties of Semicrystalline Copolyimides Based on 4,4′-Diaminodiphenylether and 1,3-Bis(4-aminophenoxy) Benzene

Copolyimides were prepared from 4,4′-diaminodiphenylether (4,4′-ODA), 1,3-bis(4-aminophenoxy) benzene (TPER), and pyromellitic dianhydride (PMDA) through a three-step imidization process with different monomer compositions. The copolymerization disrupted the molecular regularity and decreased the intermolecular interaction of the polyimide chains. The X-ray diffraction (XRD) results indicated the prepared copolyimides showed the same semicrystalline character, but had various crystallinity and crystal forms. The copolymerization also changed the crystal morphologies of the polyimides. With increasing TPER ratio, the copolyimides started to form spherulites and hedrites, which then tended to grow more perfectly as the TPER ratio was further increased. The solubility of the copolyimides and their dependence on the crystallnity and the chain flexibility was investigated. These copolyimides exhibited excellent thermal and thermo-oxidative stability.     

New luminescing complexes of Pd(II) with 2-(phenyl)benzothiazolate

The luminescent properties of the complexes [PdBt(μ-Cl)]₂, [PdEnBt]ClO₄, and [PdBryBt]PF₆ (where Bt is 2-(phenyl)benzothiazolate-N,C²′-ion, En is 1,2-(diamine)ethane, and Bpy is 2,2′-bipyridyl) are studied and a qualitative diagram of their electronically excited states is presented.     

Influence of carrier-injection efficiency on modulation rate of organic light source

We have investigated the relationship between the energy levels of an emissive layer and the modulation rate of organic light-emitting diodes (OLEDs) based on a distyrylbenzene derivative, 1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl]benzene (DSB). By utilizing DSB as an emitting material, a high modulation rate can be realized because of the short fluorescence lifetime of 0.2 ns of DSB. Furthermore, we also found that an energy gap between an emissive layer and an adjacent organic layer is an important parameter to improve modulation rate. DSB-doped 4,4-bis(2,2-ditolylvinyl)biphenyl is the best combination of all the organic materials used in this study, and the fastest cutoff frequency of 10 MHz has been achieved for the OLED in spite of the large emitting area of 1 mm(2).     

New spiro[benzotetraphene-fluorene] Derivatives: Synthesis and Application in Sky-Blue Fluorescent Host Materials

Blue light-emitting spiro[benzotetraphene-fluorene] (SBTF)-based host materials, 3-(1-naphthyl)-10-naphthylspiro[benzo[ij]tetraphene-7,9′-fluorene] (1), 3-(2-naphthyl)-10-naphthylspiro[benzo[ij]tetraphene-7,9′-fluorene] (2), and 3-[2-(6-phenyl)naphthyl]-10-naphthylspiro[benzo[ij]tetraphene-7,9′-fluorene] (3) were designed and prepared via multi-step Suzuki coupling reactions. Introducing various aromatic groups into SBTF core lead to a reduction in band gap and a determination of the color purity and luminescence efficiency. Typical sky-blue fluorescent organic light emitting diodes with the configuration of ITO/N,N′-di(1-naphthyl)-N,N′-bis[(4-diphenylamino)phenyl]-biphenyl-4,4′-diamie (60 nm)/N,N,N′,N′-tetra(1-biphenyl)-biphenyl-4,4′-diamine (30 nm)/host: dopant (30 nm, 5 %)/LG201 (electron transporting layer, 20 nm)/LiF/Al were developed using SBTF derivatives as a host material and p-bis(p-N,N-diphenyl-aminostyryl)benzene (DSA-Ph) as a sky-blue dopant material. A device obtained from three materials doped with DSA-Ph showed color purity of 0.148 and 0.239, a luminance efficiency of 7.91 cd/A, and an external quantum efficiency >4.75 % at 5 V.     

Spectroscopy and photophysics of binuclear ruthenium(II) complexes with nitrogen-containing heterocyclic bridging ligands

The absorption spectra at room temperature and the spectra, the quantum yields, and the decay times of the luminescence at 77 K of binuclear complexes [X(bpy)₂Ru(BL)Ru(bpy)₂Cl]²⁺ (bpy = 2,2′-bipyridyl; X = Cl, BL = pyrazine, 4,4′-bipyridyl, trans-1,2-bis(4-pyridyl)ethylene, and trans-1,2-bis(4-pyridyl)ethane and X = NO₂, BL = 4,4′-bipyridyl) in alcoholic (4: 1 EtOH-MeOH) solutions are studied. It is shown that the interaction between the metal centers (MCs) of the complexes affects the characteristics of the electronically excited states (EESs) of each of them and facilitates increasing the transition dipole moment Ru(d_π)→BL(π_*). The deactivation rate constants of the lowest electronically excited metal-to-ligand charge transfer (³MLCT) state of the complexes are determined. In an asymmetric binuclear complex, the energy transfer from MC(NO₂) to MC(Cl) is revealed, with the rate constant of this transfer being not smaller than 3.2 × 10¹⁰ s^?1.     

Synthesis and Characterization of Triphenylethylene Derivatives with Aggregation-Induced Emission Characteristics

New aggregation-induced emission (AIE) compounds derived from triphenylethylene were synthesized. The thermal, photophysical, electrochemical and aggregation-induced emissive properties were investigated. All the compounds had strong blue light emission capability and good thermal stability. Their maximum fluorescence emission wavelengths were between 443 to 461 nm in solid states, while their glass transition temperatures ranged from 86 to 129 °C. The decomposition temperatures of the synthesized compounds were in the range of 432–534 °C. The synthesized compounds possessed aggregation-induced emission properties, namely exhibited enhanced fluorescence emission in aggregated states. The highest occupied molecular orbital (HOMO) energy levels estimated from the oxidation potentials were between 5.61 and 5.66 eV and the lowest unoccupied molecular orbital/highest occupied molecular orbital (LUMO/HOMO) energy gap values were found to be in the range of 3.18–3.22 eV. The compounds 4-(4-(2,2-bis(4-(naphthalen-1-yl)phenyl)vinyl)phenyl) dibenzothiophene [(BN)₂Bt] and 4-(4-(2,2-di(biphenyl-4-yl)vinyl)phenyl) dibenzothiophene [(BB)₂Bt] exhibited vibronic fine-structure photoluminescence spectra when the water fraction was less than 70%.     

共轭低聚物中光生分子间电荷转移态的第一性原理研究

We perform density functional theory calculations to investigate the polaron pair (charge transfer state) photo-generation in donor-acceptor oligomer methyl-capped (4,7-benzo[2,1,3]thiadiazole-2,6-(4,4-bis (2-ethylhexyl)-4H-cyclopenta[1,2-b;3,4-b'']dithiophene-4,7-benzo[2,1,3]thiadiazole)(CPDTBT).Results show that effective photo-generation of charge transfer state can happen in CPDTBT dimer when the group 4,7-benzo[2,1,3]thiadiazole (BT) in one monomer deviates against the conjugated plane (onset torsion angle is about 20°).The lower excitation energy (530 nm) can only generate the intramolecular excitonic state,while the higher excitation energy (370 nm) can generate the intermolecular charge transfer state,in good agreement with the experiment.Moreover,the mechanism of charge separation in CPDTBT oligomers is discussed.     

Low voltage red phosphorescent organic light-emitting devices with triphenylphosphine oxide and 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl electron transport layers

We have developed red phosphorescent organic light-emitting devices operating at low voltages by using triphenylphosphine oxide (Ph₃PO) and 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi) electron transport layers. 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) and tris-(1-phenylisoquinolinolato-C²,N) iridium(III) [Ir(piq)₃] were used as host and guest materials, respectively. Small voltage drops across the electron transport layers and direct injection of holes from 4,4′,4″-tris[N-(2-naphthyl)-N-phenyl-amino]-triphenylamine (2-TNATA) hole transport layer into the Ir(piq)₃ guests are responsible for the high current density at low voltage, resulting in a high luminance of 1000 cd/m² at low voltages of 2.8–3.0 V in devices with a structure of ITO/2-TNATA/CBP:Ir(piq)₃/DPVBi/Ph₃PO/LiF/Al.     

以联苯乙烯衍生物为发光层的蓝色有机发光二极管特性的研究

以一种新型联苯乙烯衍生物NPVBi作为发光层，制备了结构为：ITO／TPD／NPVBi/Alq3/LiF/Al的有机薄膜电致发光器件，其中TPD厚度保持为50nm,NPVBi与Alq3厚度之和保持为50nm。通过调节NPVBi与Alq3的厚度，获得了色纯度较好的NPVBi蓝色电致发光，最高亮度为708cd/m^2，最大流明效率为1.13lm/W。结果表明，发光层NPVBi和电子传输层Alq3的厚度对器件的发光特性有显著的影响。     

Deep-Red Phosphorescent Iridium(III) Complexes Containing 1-(Benzo[b] Thiophen-2-yl) Isoquinoline Ligand: Synthesis,Photophysical and Electrochemical Properties and DFT Calculations

Four new bis-cyclometalated iridium(III) complexes, [Ir(btq) ₂phen] [PF₆] (3a), [Ir(btq) ₂bpy] [PF₆] (3b), [Ir(btq) ₂dtbipy] [PF₆] (3c) and [Ir(btq) ₂pic] (3d) (btq?=?1-(benzo[b] thiophen-2-yl) isoquinoline, phen?=?1,10-phenanthroline, bpy?=?2,2′-bipyridine, dtbipy?=?4,4′-di-tert-butyl-2,2′-bipyridine, pic?=?picolinic acid) have been synthesized and fully characterized. The crystal structure of 3a has been determined by X-ray analysis. The photophysical and electrochemical properties of these new complexes 3a???3d have been studied. The photoluminescence spectra of all Ir(III) complexes exhibit deep-red emission maxima at 682, 682, 683 and 698 nm, respectively. The most representative molecular orbital energy-level diagrams and the lowest energy electronic transitions of 3a???3d have been calculated with density functional theory (DFT) and time-dependent DFT (TD???DFT). The results show that the pic ancillary ligand of complex 3d influences the absorption and emission energies with a further red-shift relative to other three complexes 3a???3c.     

Solution-processed white organic light-emitting devices based on small-molecule materials

We investigated solution-processed films of 4,4′-bis(2,2-diphenylvinyl)-1,1′-bibenyl (DPVBi) and its blends with N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) by atomic force microscopy (AFM). The AFM result shows that the solution-processed films are pin-free and their morphology is smooth enough to be used in OLEDs. We have developed a solution-processed white organic light-emitting device (WOLEDs) based on small-molecules, in which the light-emitting layer (EML) was formed by spin-coating the solution of small-molecules on top of the solution-processed hole-transporting layer. This WOLEDs, in which the EML consists of co-host (DPVBi and TPD), the blue dopant (4,4′-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl) and the yellow dye (5,6,11,12-tetraphenylnaphtacene), has a current efficiency of 6.0 cd/A at a practical luminance of 1000 cd/m², a maximum luminance of 22500 cd/m², and its color coordinates are quite stable. Our research shows a possible approach to achieve efficient and low-cost small-molecule-based WOLEDs, which avoids the complexities of the co-evaporation process of multiple dopants and host materials in vacuum depositions.     

Influence of bridging atom on the vertical phase separation of low band gap bulk heterojunction solar cells

Vertical phase separation of the polymer and fullerene molecules in bulk heterojunction organic solar cells influences the exciton dissociation, charge carrier transport and collection. This work compares the vertical phase separation of poly[2,1,3‐benzothiadiazole‐4,7‐diyl[4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta [2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl]] (C‐PCPDTBT):[6,6]‐phenyl C71 butyric acid methyl ester (PC₇₁BM) and poly[2,1,3‐benzothiadiazole‐4,7‐diyl[4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta [2,1‐b:3,4‐b′]dithiophene‐siloe2,6‐diyl]] (Si‐PCPDTBT):PC₇₁BM blend films, using X‐ray photoemission spectroscopy depth profiles. The difference between the two polymers is the bridging atom, which is carbon for C‐PCPDTBT and silicon for Si‐PCPDTBT. Si‐PCPDTBT exhibits enhanced polymer chain packing and crystallinity. We believe this enhanced chain packing provides a driving force during film drying which alters the vertical morphology. The different nature of vertical phase separation plays a role in determining the increased device performance observed for Si‐PCPDTBT:PC₇₁BM solar cells. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Spectroscopy and photophysics of chloro-bis-bipyridyl complexes of ruthenium(II) with pyridine ligands

The absorption, luminescence, and luminescence excitation spectra of ruthenium(II) complexes cis-[Ru(bpy)₂(L)Cl]⁺[bpy=2,2′-bipyridyl; L=NH₃, pyrazine, pyridine, 4-aminopyridine, 4-picoline, isonicotinamide, 4-cyanopyridine, 4,4′-bipyridyl, or trans-1,2-bis(4-pyridyl)ethylene] in alcoholic (4: 1 EtOH-MeOH) solutions are studied. At 77 K, the quantum yields and decay times of the luminescence of the complexes are measured and the deactivation rate constants of the lowest electronically excited metal-to-ligand charge transfer state (³MLCT) are determined. The linear correlation between the energy of the lowest state ³MLCT d _π(Ru)>π*(bpy) of the cis-[Ru(bpy)₂(L)Cl]⁺ complexes and the parameter pK_a of the free 4-substituted pyridines and pyrazine used as ligands is established.     

Preparation of Main-Chain Thermotropic Polyesters With Two Types of Mesogens Connected Alternatively by Aliphatic Spacers

A homologous series of main-chain thermotropic polyesters (PBTn, n = 2, 4, 6) containing biphenyl and triad aromatic ester mesogenic units interconnected by n-methylene spacers in the main chain were prepared from terephthaloyl bis(4-oxybenzoyl chloride) (TOBC) and 4,4′-bis(ω-hydroxyalkyloxy)biphenyls (n-BP, n = 2, 4, 6) by solution polycondensation. The chemical structures of the monomers and PBTn were characterized by spectroscopic techniques and elemental analysis. The solubility, supermolecular structures, thermal and liquid crystalline properties of PBTn were investigated by differential scanning calorimetry (DSC), polarizing microscopy (PLM), small-angle X-ray scattering (SAXS), thermogravimetric analyses (TGA), and wide-angle X-ray diffraction (WAXD), and they were found to be closely dependent on the length of the methylene spacers. The increasing methylene units led to improved solubility, broader liquid crystalline range, reduced mesophase-isotropic transition point, higher thermal stability, and decreasing crystallinity. The decomposition temperatures (5% mass loss) of the polymers were above 380°C in nitrogen atmosphere and only PBT4 and PBT6 exhibited smectic mesophases as well as high viscosity in the mesophase.