Search

The quartz tube solid particle air receiver is a new type of solar receiver in which fluidized particles absorb the solar radiation directly and heat the air effectively, improving the efficiency of solar thermal power generation and reducing costs. In this article, transient numerical simulation was conducted to simulate the heat transfer and flow processes in single quartz tube under concentrated solar radiation. The results showed that the distribution of solid particles temperature was uniform in the fluidized region, which could overcome the problem of overheating in the volumetric solar receiver. The temperature difference between solid particles and air was no more than 25K, indicating that heat transfer between particles and air was very effective. Further, as the direct solar radiation increased, the average air temperature in the outlet increased while the thermal efficiency decreased. The high tube wall temperature caused heat loss to the environment by radiative and convective heat transfer. With the air inlet velocity increasing, the averaging air temperature in the outlet decreased while the efficiency of the receiver increased. The simulation results provided important reference for improving the performance of the quartz tube solid particle air receiver.

Three solution-processable red-emissive organic materials with a hole-transporting unit triphenylamine (TPA) as the core part and a D-pi-A bipolar structure as the branch part, TPA-BT (single-branched molecule), b-TPA-BT (bibranched molecule), and t-TPA-BT (tribranched molecule), were synthesized by the Heck coupling reaction. Herein, for the D-pi-A push-pull structure, we use TPA as the electron donor, benzothiodiazole (BT) as the electron acceptor, and the vinylene bond as the pi-bridge connecting the TPA and BT units. The compounds exhibit good solubility in common organic solvents, benefited from the three-dimensional spatial configuration of TPA units and the branch structure of the molecules. TPA-BT, b-TPA-BT, and t-TPA-BT show excellent photoluminescent properties with maximum emission peaks at ca. 630 nm. High-performance red-emission organic light-emitting diodes (OLEDs) were fabricated with the active layer spin coated from a solution of these compounds. The OLED based on TPA-BT displayed a low turn-on voltage of 2.0 V, a maximum luminance of 12192 cd/m2, and a maximum current efficiency of 1.66 cd/A, which is among the highest values for the solution-processed red-emission OLEDs. In addition, high-performance white-light-emitting diodes (WLEDs) with maximum luminance around 4400 cd/m2 and maximum current efficiencies above 4.5 cd/A were realized by separately doping the three TPA-BT-containing molecules as red emitter and poly(6,6'-bi-(9,9'-dihexylfluorene)- co-(9,9'-dihexylfluorene-3-thiophene-5'-yl)) as green emitter into blue poly(9,9-dioctylfluorene-2,7-diyl) host material with suitable weight ratios.

Well-defined poly(N-isopropyl acrylamide) (PNIPAAm) brushes on commercial hydrophobic poly(vinylidene fluoride) (PVDF) microfiltration membrane surfaces were prepared, via direct atom transfer radical polymerization (ATRP) with the secondary fluorinated site of PVDF as initiator and water as solvent at 80°C. The effect of solvents on the ATRP was studied in detail. The water as reaction solvent was in favor of surface-initiated ATRP of N-isopropyl acrylamide (NIPAAm) from secondary fluoride of PVDF membranes. The chemical composition and structure of the modified PVDF membrane surfaces were determined by attenuated total reflectance (ATR) Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The surface and cross-section morphology of membranes were studied by scanning electron microscopy (SEM). The pore sizes of the pristine PVDF membrane and the PNIPAAm-grafted PVDF membranes were measured using micro-image analysis and process software. The introduction of the well-defined PNIPAAm on the PVDF membrane gave rise to hydrophilicity. Water contact angles of PVDF membranes reduced after the surface grafting of PNIPAAm. Water fluxes and protein solution permeation experiments revealed that the PNIPAAm-grafted PVDF membranes exhibited temperature-responsive permeability. The unique microstructure of PNIPAAm brushes facilitated hydrophilicity below the lower critical solution temperature.

Novel cylindrical polymer brushes consisting of poly(diphenylacetylene) main chain and poly(poly(ethylene glycol) methyl ether monomethacrylate) (PPEGMA) side chains were synthesized by the diphenylacetylene macromonomer or side chain initiated atom transfer radical polymerization (ATRP) of poly(ethylene glycol) methyl ether monomethacrylate (PEGMA) from an bromo isobutyryl-bearing poly(diphenylacetylene) (poly(BrDPA)) method. The diphenylacetylene macromonomer, namely, DPA–PPEGMA, were prepared by the ATRP of PEGMA from bromo isobutyryl-bearing diphenylacetylene. DPA–PPEGMA was polymerized successfully with WCl6–Ph4Sn catalyst to give high molecular weight polymer brushes poly(DPA–PPEGMA). Meanwhile, polymer brushes (PDPA-g-PPEGMA) were obtained by ATRP of PEGMA from poly(BrDPA). The molecular weight of the side chains of PPEGMA could be controlled simply by modulating the ATRP time. The macromonomer and polymer brushes are soluble in nonpolar solvents such as toluene and chloroform. The polymers of poly(BrDPA) and poly(DPA–PPEGMA) absorb in the longer wavelength region, with two peaks at around 370 and 414 nm. The polymers are thermally stable and exhibit double crystallization and melting peaks during the cooling and heating scans.

Strong intermolecular interactions usually result in decreases in solubility and fluorescence efficiency of organic molecules. Therefore, amorphous materials are highly pursued when designing solution-processable, electroluminescent organic molecules. In this paper, a non-planar binaphthyl moiety is presented as a way of reducing intermolecular interactions and four binaphthyl-containing molecules (BNCMs): green-emitting BBB and TBT as well as red-emitting BTBTB and TBBBT, are designed and synthesized. The photophysical and electrochemical properties of the molecules are systematically investigated and it is found that TBT, TBBBT, and BTBTB solutions show high photoluminescence (PL) quantum efficiencies of 0.41, 0.54, and 0.48, respectively. Based on the good solubility and amorphous film-forming ability of the synthesized BNCMs, double-layer structured organic light-emitting diodes (OLEDs) with BNCMs as emitting layer and poly(N-vinylcarbazole) (PVK) or a blend of poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] and PVK as hole-transporting layer are fabricated by a simple solution spin-coating procedure. Amongst those, the BTBTB based OLED, for example, reaches a high maximum luminance of 8315 cd · m−2 and a maximum luminous efficiency of 1.95 cd · A−1 at a low turn-on voltage of 2.2 V. This is one of the best performances of a spin-coated OLED reported so far. In addition, by doping the green and red BNCMs into a blue-emitting host material poly(9,9-dioctylfluorene-2,7-diyl) high performance white light-emitting diodes with pure white light emission and a maximum luminance of 4000 cd · m−2 are realized.

A newly and interestingly small organic molecule, (R)-2,2′-dimethoxyl-3,3′-di(phenyl-4-yl-diphenyl-amine)-[1,1′]-binaphthyl, was introduced into solid-state electrolyte to assemble dye-sensitized photoelectrical cell. With optimized molecular structure and composite porous TiO 2 electrode, the solid-state device without any additives in electrolyte converted light to electric efficiency with a 0.07%. Under the assistance of some functional small-molecules in the electrolyte, solid-state devices showed an attractive conversion efficiency of 0.55%. In addition, the positive effects of functional additives on the photoelectrical performance, such as inhibiting interface charge recombination, improving hole-transporting properties and penetration of solid-state electrolyte, were discussed experimentally and theoretically in detail.

Spectroscopic properties of new hyperbranched conjugated polymers functionalized in periphery with N,N-dimethylaniline and tert-butyl-benzene as terminal groups are investigated by one- and two-photon excitations. The absorption, fluorescence excitation and emission spectra are examined in chloroform and N,N-dimethylformamide. The two-photon excitation measurements show that the new hyperbranched conjugated polymer possesses large two-photon excitation cross section which makes it a very attractive candidate for the potential application as nonlinear optical materials. As an example, the two-photon induced three-dimensional data storage is also demonstrated.

A material compound, 9,9-bis{4′-[2″-(carbazolyl)-vinyl]-phenyl}fluorene (F-CZV), was specially synthesized and used to fabricate the efficient white organic light-emitting devices (WOLEDs). The absorption peaks appear at 340 nm and 346 nm in dilute dichloromethane solution and film, respectively. The photoluminescence peaks appear at 350 nm and 400 nm in the solution and film, respectively. Photoluminescent quantum yield in solution is ca 0.82 by using quinine sulfate as the standard. In an optimized electroluminescent device structure of ITO/NPB (40 nm)/F-CZV (30 nm)/BPhen (40 nm)/Mg:Ag, the saturated white-light emission was observed at Commission International De L’Eclairage (CIE) coordinates of (0.30, 0.33) at 10 V. The El spectrum of the device is close to independent of the applied driving voltage. It’s maximum brightness and current efficiency is 700 cd/m 2 and 0.41 cd/A, respectively.

Three kinds of novel organic materials containing binaphthyl units, BNOBPV, BNONV and BNOAV, were synthesized by Wittig–Horner reactions. Their photophysical and electroluminescent (EL) properties were studied. BNOBPV and BNONV exhibited pure blue light as emitting materials in organic light-emitting diodes (OLED) with EL spectra peaked at 444 nm and CIE coordinates around (0.157, 0.095) and (0.171, 0.112), respectively. BNOAV showed a red-shifted emission peaked at 496 nm, which may be ascribed to the contribution of anthracene moieties.

An organic compound with two triphenylamine moieties linked with binaphthyl at the 3,3'-positions (2,2'-dimethoxyl-3,3'-di(phenyl-4-yl-diphenyl-amine)-[1,1']-binaphthyl, TPA-BN-TPA) can be synthesized by Suzuki coupling. Amorphous and homogeneous films are obtained by either vacuum deposition or spin-coating from solution in good solvents, while single crystals are grown in an appropriate polar solvent. X-ray crystallography showed that a TPA-BN-TPA crystal is a multichannel structure containing solvent molecules in the channels. The intramolecular charge-transfer state resulting from amino conjugation effects is observed by solvatochromic experiments. The high glass-transition temperature (130 °C) and decomposition temperature (439 °C) of this material, in combination with its reversible oxidation property, make it a promising candidate as a hole-transport material for light-emitting diodes. With TPA-BN-TPA as the hole-transporting layer in an indium tin oxide/ TPA-BN-TPA/aluminum tris(8-hydroxyquinoline)/Mg:Ag device, a brightness of about 10100 cd m -2 at 15.6 V with a maximum efficiency of 3.85 cd A -1 is achieved, which is superior to a device with N,N'-di(1-naphthyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine as the hole-transporting layer under the same conditions. Other devices with TPA-BN-TPA as the blue-light-emitting layer or host for a blue dye emitter are also studied.

In this paper, the optical and photo-induced electron transfer properties of a new conjugated molecule, 4,7-bis{5′-[4″,4″- N , N -diphenylamino-styryl]thiphen-2′-yl} -benzo[1,2,5-thiadiazole] (simplified as TPA-th-TPA), were investigated. Using TPA-th-TPA as a photoactive layer, organic solar cells with three different architectures were fabricated by spin-coating method. The photosensitive layers of these architectures comprise pure TPA-th-TPA layer, heterojunction of bi-layered TPA-th-TPA and C 60 , and bulk-heterojunction of TPA-th-TPA and [6, 6]-phenyl C 61 -butyric acid methyl ester (PCBM) blend. Furthermore, towards the bulk-heterojunction devices, the effect of the cathode materials (Mg, Ca, LiF/Al, Ba) on the performance of the devices was studied. The power conversion efficiency reached 0.26% for the device based on the blend of TPA-th-TPA and PCBM with Ba/Al as the cathode.

Poled polymers are currently of great interest in second-order nonlinear optical (NLO) applications such as electro-optic (EO) modulation, optical switching, etc. The EO active chromophores doped in polymer matrices generally have large dipole moment. The strong electrostatic interaction between molecular dipoles causes orientation relaxation after poling, decrease of poling efficiency, phase separation, and etc. at high doping concentration. A new type of NLO chromophore with low ground-state dipole moment has been designed and synthesized. It was doped in PMMA polymer matrix. The electrostatic interaction between chromophore molecules in this doped film is reduced greatly. This provides a way to increase the doping level in guest-host poled polymer system. At a very high loading level of 52% wt. (N = 6.41 × 1020/ cm 3), which is over 2 times of the theoretically predicated value for the spherical shape molecules, reasonable film quality and dipole orientation stability have been achieved.

Two series of hyperbranched conjugated polymers were synthesized via an A 3 + B 2 type Wittig reaction. The molecular weights of the polymers were successfully tuned by simply changing the feed ratio of the monomers. Polymers with higher molecular weights presented more efficient photoluminescence, higher thermal stability and higher performance of LEDs.

The formation of a cylinder-like helical conformation induced by solvation was observed from a conjugated polymer poly(N-octylcarbazole ethylene). The polymer was synthesized by McMurry condensation using N-octyl-3,6-diformylcarbazole as monomer, in which the alkylcarbazolyl group was functioned as a turn angle. IR analysis indicated that the double bond in the polymer chain mainly takes a cis- conformation. Computer simulation revealed that the polymer could form into a hollow tubular nano-structure with a cavity of less than 1 nm in diameter by folding its strand. The helical conformation formed by solvent induction was further proved by the measurements of circular dichroism (CD) spectrum, specific rotatory power and fluorescent (FL) spectra. Copyright © 2006 John Wiley & Sons, Ltd.

Two series of novel ternary copolyimides containing perylene and fluorene units in the backbone were synthesized by one-step polycondensation of diamine (4,4′-(9H-fluoren-9-ylidene)bisphenylamine, FBPA) with perylene dianhydride (3,4,9,10-perylenetetracarboxylic dianhydride, PTCDA) and a comonomer [4,4′-(hexafluoroisopropylidene) diphthalic anhydride, 6FDA or 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, BDTA]. The polymers were named as PFFx (PTCDA-FBPA-6FDA) and PFBx (PTCDA-FBPA-BTDA), respectively, and their chemical structures were identified by FT-IR spectra and elemental analyses. Perylene contents in the copolyimides were determined through a quantitative UV-vis spectroscopy method, which are in agreement with the values calculated from the added raw materials both for PFFx and PFBx. Gel permeation chromatography (GPC) measurement suggested that the weight average molecular weight (Mw) is in the range 2.1–5.09 × 104 and the molecular weight distribution (MWD) is 1.86–2.72 for PFFx, and those for PFBx are 2.64–4.73 × 104 and 2.44–2.92, respectively. Thermogravimetric analysis (TGA) measurements showed that the copolyimides are very thermally stable with a temperature of 10% weight loss (T10) in the range 546–563°C for PFFx, and 538–548°C for PFBx. The copolyimides also have good solubility in common organic solvents such as chloroform and tetrahydrofuran. These unique properties can be attributed to the existence of the bulky diphenylfluorene moieties in the polymer backbone. All the copolyimides can emit strong fluorescence both in solution and in films, which make them possibly be used as thermostable light-emitting materials for organic light-emitting diodes. Copyright © 2006 John Wiley & Sons, Ltd.

A novel alternating conjugated copolymer (poly[(dioctyloxyphenylene vinylene)-alt-(2,1,3-benzothiadiazole)], C8-PPV-BT) consisting of electron-rich dioctyloxybenzene and electron-deficient 2,1,3-benzothiadiazole repeat units was synthesized via a Pd-catalyzed Heck cross:coupling polycondensation. The thermal, electrochemical, qptical properties, and phntophysics of C8-PPV-BT blended with [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) have been investigated, Photovoltaic devices of ITO/PEDOT-PSS/C8-PPV-BT + PCBM (1/4, w/w)/Bh/Al were fabricated and their photovoltaic parameters were measured. The results showed the energy conversion efficiency (η e ) and external quantum efficiency (EQE) were 0.335 and 11.7% (451 nm), respectively, under simulated solar light illumination having light intensity of 78.2 mW.(cm 2 )- (AM1.5), which were both higher than those of devices based on poly[(dioctyloxyphenylene ethynylene)-alt-(2,1,3-benzothiadiazole)] (C8-PPE-BT) and PCBM blend under the same conditions. Optical, electrochemical, and photovoltaic properties of C8-PPV-BT and C8-PPE-BT copolymers were also compared and discussed.

A novel alternating conjugated polymer (C12-PPE-BT) containing phenylene-ethynylene and benzothiadiazole (BT) units (unless otherwise specified, C12-PPE-BT is represented that the BT ratio is 50% (mol%)) was synthesized by cross-coupling polycondensation with bis (triphenylphosphine)-dichloropalladium (Pd(PPh 3 ) 2 Cl 2 ) and phase transfer catalyst(PTC). C12-PPE-BT was characterized by 1 H NMR, IR, TGA, DSC and elemental analysis. Its electrochemistry, photophysics and electroluminescence properties were discussed. The copolymer obtained possesses high thermal stability, high oxidation and reduction potentials, and high photoluminescence quantum yield. Devices based on C12-PPE-BT copolymer emit red light with λ max = 620 nm. The emission of phenylene-ethynylene segments almost completely disappeared manifested that the intrachain and/or interchain energy transfer from phenylene-ethynylene segments to BT units occurred.

A novel poly(p-phenylene vinylene) (PPV)/ poly(p-phenylene ethynylene) (PPE) block-copolymer was synthesized by a cross-coupling polycondensation with Pd(PPh 3 ) 2 Cl 2 and a phase-transfer catalyst, and was confirmed by 1 H NMR and IR spectroscopy and elemental analysis. The thermal, electrochemical, and photoluminescent properties of the new copolymer have been investigated. The incorporation of triple bonds into the cyano-substituted PPV (CN-PPV) backbone leads to higher oxidation and reduction potentials than poly(2-methoxy-5-(2-ethylhexyloxy)-p-phenylene vinylene) (MEH-PPV) and CN-PPV, potentially making the copolymer a good electron-transporting material for use in a light-emitting-diode device.

An alternating copolymer containing triphenylamine (TPA) and cyano-substituted benzene moieties, TPA-CNPPV was synthesized using the Wittig reaction. The monomers and polymer were characterized by H-NMR, FT-IR and mass spectroscopy (MS). The polymer shows good solubility in common organic solvents and excellent film-forming ability. Thermogravimetric analysis (TGA) demonstrates that the polymer has a degradation temperature (TD) of 600°C; differential scanning calorimetry (DSC) result indicates that the glass transition temperature (Tg) of TPA-CNPPV is 160°C, suggesting high thermal stability. The photophysical properties of the light-emitting material were investigated in both solution and spin-coated film. Photo-isomerization of the polymer was investigated by UV-vis and fluorescence spectra. The interaction between TPA-CNPPV and C60 was studied by fluorescence quenching. Copyright © 2004 John Wiley & Sons, Ltd.

The luminescent copolymer 2-phenyl-5-[3′-(methacrylamido)phenyl]-1,3,4-oxadiazole and vinylcarbazole (PMAPO–VCZ), combining hole-facilitating moiety, carbazole ring, and electron-facilitating moiety, 1,3,4-oxadiazole, as side groups, was synthesized by a radical polymerization of the olefinic monomer PMAPO and VCZ. For comparison, the homopolymer P-PMAPO was also synthesized by similar procedures. The solubility, thermal, and optical properties of the copolymers were investigated. The synthesized copolymer was soluble in common organic solvents but the homopolymer of PMAPO was dissolved only by hot THF. Thermogravimetric analysis and differential scanning calorimetry measurements showed that the copolymer and homopolymer exhibit good thermal stability up to 360 and 340°C with glass-transition temperatures higher than 105 and 65°C, respectively. The photoluminescence properties were investigated. The results showed that the copolymer emits blue and blue-green light and the emission spectra of monomer and polymers exhibit obvious solvent effect. With the increase of polarity of solvents, the fluorescence spectra distinctly change, appearing with a red shift at room temperature. The concentration-dependent emission spectra change significantly with the increase of concentration. In addition, when N,N-dimethylaniline (DMA) was gradually added to the solution of copolymers, the emission intensity of fluorescence was dramatically increased. However, when the concentration of DMA was increased beyond a certain level, the emission intensity of fluorescence gradually decreased. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2777–2783, 2004

A novel copolymer has been synthesized by copolymerization of 2,2′-dimethacrylamido-1,1′-binaphthyl (DMBN) with vinylcarbazole (VCZ) and its fluorescence characterization has been studied. The results show that the copolymer (DMBN-VCZ) is soluble in some common organic solvents and the fluorescence of the copolymer (DMBN-VCZ) can be quenched by both electron donors and electron acceptors where the quenching effects follow the Stern–Volmer equation. The dimolecular exciplexes between copolymer (DMBN-VCZ) and strong electron donor or electron acceptor are formed. Moreover, the interaction between copolymer (DMBN-VCZ) and C60 is also studied by fluorescent quenching. Copyright © 2004 John Wiley & Sons, Ltd.

Three hyperbranched phenylene vinylenes (HPVs)—H-mn, H-es, and H-py—were used in fabricating polymer photovoltaic cells (PVCs). PVCs with photoactive layers composed of pure HPV, a blend of HPV and C60, and a blend of HPV, poly(2-methoxyl-5,2′-ethylhexyoxyl-1,4-phenylene vinylene) (MEH-PPV), and C60, were fabricated, and their current–voltage characteristics were measured and investigated. The PVC with photoactive layers composed of H-es and C60 showed promising photovoltaic characteristics, with an energy-conversion efficiency of 0.035%, when illuminated under 85 mW/cm2 white light. The short-circuit current and energy-conversion efficiency of the PVCs based on H-mn/C60 and H-py/C60 were greatly improved when they were blended with a small amount of MEH-PPV. The incident photon-to-collected-electron efficiency of the HPV/MEH-PPV/C60 PVCs indicated that both HPVs and MEH-PPV contributed to the photocurrent. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1459–1466, 2004

The photovoltaic applications of conjugated polymer/fullerene composites have attracted much attention from the scientific community. The photoinduced electron transfer and other related photophysical processes occurred in the composites are the central issues. Several kinds of conjugated polymers have been synthesized in our laboratory. Studies of their composites with fullerene are reviewed. We observed strong fluorescence quenching of these conjugated polymers on mixing them with C60 in dilute solution. Anion radical species of C60 were observed in ESR measurements as a result of photoinduced charge separation. The quenching constants vary with different conjugated polymers and thus provide a quantum measurement for the interaction between the donor and acceptor. Solar cells have been fabricated from these conjugated polymer/fullerene composites. Energy conversion efficiency up to 1.1% has been achieved.

Perylene-3,4,9,10-tetracarboxylic acid (PTCA) was found to form stable Langmuir films at the air/water interface through the coordination with Cu(II) ion in the subphase although the compound itself could not form monolayer on a plain water surface. The Langmuir films can be transferred onto solid substrates by a Langmuir–Schaefer (LS) method. Surface pressure–area isotherm and measurement of the UV–Vis and FT-IR spectra of the transferred LS films confirmed the coordination between the carboxylic group and Cu(II) ion in the Langmuir films. Atomic force microscopy (AFM) measurements indicated that the Langmuir film was composed of small nanoparticles with a diameter of several tens of nanometers. X-ray diffraction (XRD) measurement on the transferred LS films revealed that the film formed a clear layer structure with a distance of 3.9 nm, which was in agreement with the height measurement from the AFM.

We report photophysical and electroluminescence (EL) properties of three novel hyperbranched phenylene vinylenes (HPVs) with benzene as the core, 2,5-dimethyloxyl substituted phenylene vinylene as the connecting unit, and benzene, dimethylaniline or pyridine as the terminal group, respectively. The absorption maxima of the HPVs blue-shift from solution to the films due to their twisted molecular conformation. The emission spectra in the films red-shift compared to those in solution, which may originate from interchain excimer species. The thin films of the HPVs exhibit pretty high photoluminescence (PL) quantum yields around 50.5–87.8%. Blue–green light-emitting electrochemical cells (LECs) based on the HPVs have been demonstrated with turn-on voltages of 2.5–2.6 V. The ac impedance measurements indicate the operation of the LECs corresponds to an electrochemical doping model.

The strategy of introducing the chromophores with low ground state dipole moment had been discussed to overcome the effect of the electrostatic interaction between the chromophores in the poled polymer films on its nonlinearity. As a result, the effective nonlinear optical coefficient d33 of the poled films, containing the chromophores with μg in the range of 3.5–5.5 D, will enhance at least 15%, even over 30%, compared to that of 7.5 D if the first hyperpolarizabilities (β) of chromophores are in the same magnitudes. And, under the above assumption, the same level of the d33 could even be achieved by utilizing the chromophores with μg as low as 2.2 D.

A multiple charge-transfer second-order nonlinear optical (NLO) chromophore 2,3-bis(4-aminophenyl)-5,6-dicyanopyrazine (BAPDCP) was successfully designed and synthesized. It was characterized by 1H NMR, mass spectrometry, Fourier transform infrared spectroscopy, and elemental analysis. The first hyperpolarizability β of BAPDCP was measured with the Hyper–Rayleigh scattering technique, which was 123.5 × 10−30 esu. The donor-embedded prepolyimide and prepolyurea were also synthesized by a polyaddition reaction. Thermogravimetric analysis and differential scanning calorimetry demonstrated that either the chromophore or the polymers have fine thermal stability. The thin films of prepolymers were prepared by coating on ITO glass substrate and poled by corona poling at elevating temperature. The second-order NLO coefficients d33 of the films were measured by in situ second-harmonic generation measurements. The d33 were deduced as 27.7 and 16.5 pm/V for polyurea and polyimide at 1064 nm fundamental wavelength, respectively. The onset depoling temperature of the polyimide and polyurea were both as high as 200 °C. To understand the temperature effect to the orientation thermal stability of polyimide, two films were treated at different final poling temperatures. The depoling experimental results showed that the orientation stability is higher, as raising the final treated temperature but the d33 value are almost similar. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2846–2853, 2003

A series of light-emitting conjugated polymers alternatively involving carbazole and bivinylene arylene moieties in the main chain were synthesized via Wittig-Horner type copolymerization. The photoinduced charge transfer process relating to these polymers was investigated by using the technique of fluorescence spectroscopy. The interaction between excited copolymers and C60 in benzene solution was studied. The fluorescence quenching can be well described by the “sphere-of-action” mechanism. It is believed that two basic steps are involved in the quenching process, i.e. the diffusion of excitation within the conjugated polymers and the dissociation of the exctions trapped by fullerene. The radius of the sphere-of-action can be related to the excitation diffusion length, which depends on the lifetime of the exciton. The dynamic fluorescence quenching of the copolymers by another quencher, 1,4-dicyanobenzene (DCB) was also surveyed. Copolymers with different chain conformations show different temperature effects in the dynamic quenching. A planar conformation is beneficial for the quenching via bimolecular collision.

Two light-emitting conjugated polymers alternatively involving arylenevinylene and a N-alkyl carbazole moieties in the main chain were investigated. The formation of an intramolecular charge transfer state was probed within the repetition units of the copolymers. A tail absorption band and dual fluorescence were found for one of the copolymers, poly[(9-(2-ethyl-hexyl)-9H-carbazol-3,6-ylene)-alt-(anthracen-9,10-ylene) vinylene], Cz-PAV. Solvent polarity effects were studied by means of steady-state spectroscopy and fluorescence-lifetime measurements. Fluorescence emission spectra at 77 K were also explored. All the results show that a photoinduced intramolecular charge transfer state was formed in Cz-PAV. The formation of this state may be related to the electron affinity of the acceptor group contained in the copolymer and to the molecular conformation of the copolymer. Copyright © 2003 John Wiley & Sons, Ltd.

Covalently-bound self-assembled monolayer of a kind of functional hyperbranched polymer, pyridine-capped hyperbranched poly(para-phenylene vinylene) (Py-HPV), was prepared on hydrophilic quartz or single-crystal silicon substrates using siloxane self-assembly techniques. The assembling procedure was characterized by contact angle measurement, X-ray photoelectron spectroscopy (XPS), UV-vis spectra and fluorescence spectroscopy. Atomic force microscopy (AFM) was also used to investigate the surface morphology and microstructure of the resulting Py-HPV self-assembled monolayer. Copyright © 2003 John Wiley & Sons, Ltd.

Two alternating copolymers containing triphenylamine and biphenyl or fluorene, poly[triphenylamine-alt-biphenylene vinylene] (TPA-PBPV) and poly[triphenylamine-alt-2,7-fluorenenylene vinylene] (TPA-FLV) were synthesized by means of the Wittig reaction. Both the polymers show good solubility in common organic solvents and excellent film-forming ability. Thermogravimetric analysis investigation demonstrates that the polymers have high thermal stability, the degradation temperature of TPA-FLV is as high as 499.0 °C. Differential scanning calorimetry results indicate that the glass transition temperature of poly TPA-FLV is higher than 200 °C, much higher than that of PBPV-TPA, which might be a merit for the long-life operation of light-emitting devices. The photophysical properties of the polymers were investigated in both CH2Cl2 solution and spin-coated film, photoluminescence efficiencies are also determined, PFV-TPA has a higher efficiency, which may make it a more promising candidate for light-emitting materials. Copyright © 2003 John Wiley & Sons, Ltd.

A series of hyperbranched polyphenylene vinylenes (HPVs) with different alkoxy substituted end groups were synthesized and characterized. The photoluminescence properties were investigated, and the cis–trans isomerization was found by prolonging the exposure time to UV light for the HPVs. The viscosity and end-group effects on the photoisomerization were studied. Copyright © 2003 John Wiley & Sons, Ltd.

Optical properties of a triphenylamine-containing anthrylenevinylene-based copolymer and its model compound were evaluated using absorption and steady-state fluorescence spectroscopy. The polymer and model compound show a strong solvatochromic shift as a function of solvent polarity, indicating the emission of an additional charge-transfer species. More direct and convincing evidences of the charge transfer, such as temperature and concentration-dependent emission, are presented. Low temperature (77 K) fluorescence also confirmed the existence of charge transfer. Additionally, a twisted intramolecular charge transfer state was observed in the model compound when excited by higher energy, which could not be observed in the polymer whatever the excitation was. The results indicate that there are more charge transfer states including intramolecular, intermolecular and interchain charge transfer states in polymers than in the model compound. Copyright © 2003 John Wiley & Sons, Ltd.

The fluorescence properties of two nitrogen-containing poly-(phenylene vinylene)-related copolymers were investigated under high pressure. Because of the large difference in interchain interaction between these two copolymers, the emission states are different from each other. Under the perturbation introduced by compression, the emission intensity exhibits different trends of change.

A novel kind of hyperbranched conjugated light emitting polymers with 2,5-dimethyloxyl substituted phenylene vinylene as the connecting units and different hole or electron transporting groups such as dimethylaniline phenylene or pyridyl phenylene as the terminal groups were synthesized by modified one step Wittig polymerization reaction. The photophysical properties in solution and in films of hyperbranched conjugated polymers were studied in details. The oxidation potentials were measured by cyclic voltammetry. It was found that the hyperbranched conjugated polymers were highly soluble in common organic solvents, with good film-forming properties. In particular, the thermal stability of HPVs is extremely higher than that of linear polyphenylene vinylene derivatives. In addition, the LED, LEC devices using hyperbranched polymer as active layer were investigated. All results show that these novel hyperbranched conjugated polymers could be good candidates for the fabrication of high performance LED and other optoelectronic devices.

The photoluminescence (PL) and electroluminescence (EL) properties of a novel copolymer PVK- co -MMA- co -Eu(BA) 2 (MAA)phen (PKMEu) were investigated. The significant difference between the PL intensities of the carbazole and the europium complex in different states is attributed to the Forster energy transfer from the carbazole groups to the Eu-complexes. The formation of excimers explained the red-shift of the PL peak of the carbazole group, when PKMEu is in a solid state. PKMEu can form good quality film by spin coating from chloroform solution. The single-layer LED based on PKMEu exhibits characteristic red electroluminescence (EL) of Eu 3+ with a turn-on forward bias of 24 V. The device reached a maximum brightness of 0.228 cd/m 2 at 29 V, with a luminous efficiency of 2.87×10 −4 lm/W. The relatively high turn-on voltage, low brightness and low efficiency may have resulted from the unbalanced charge–transport and the conditions of device fabrication.

A series of novel hyperbranched conjugated luminescent polymers with different length of alkyloxy substitution were designed, synthesized, and characterized by FT-IR, 1H-NMR, 13C-NMR and gel permeation chromatography (GPC). Their special photophysical properties can be attributed to their hollowed and twisted structure. Their electrochemical and electroluminescent properties were investigated. The maximum quantum efficiency of light emitting device (LED) made from C1-HPV is 0.02% at 15 V. Copyright © 2002 John Wiley & Sons, Ltd.

A novel hyperbranched conjugated polymer composed of 1,3,5-trivinylicbenzene cores and (2,5-dimethoxyl)-1,4-phenylenevinylene connecting units (HB2) was synthesized via Wittig reaction route. The resulting polymer has good solubility in common organic solvents due to its weak intermolecular interaction and low solvation energy. PL and EL properties of HB2 were inspected. In film, absorption of HB2 was slightly blue shifted from absorption in solution while PL emission was red shifted from that of solution. These marked differences suggested a large change in inter- and/or intra-molecular interaction from solution to solid film. Single layer light emitting diodes were fabricated utilizing HB2 as the emitting layer. Dispersing HB2 into a PVK matrix caused significant changes in the device performance. Bright blue emission >800 cd/m 2 can be achieved at a bias of 24 V for the ITO/PVK:HB2=5:1/Ca/Al devices and efficiency of the polymer blend devices was an order of magnitude higher than that of the HB2 single layer devices.

On the basis of a series of hyperbranched conjugated polymers (HPV) synthesized in our laboratory, the composition of HPV with nanosized cadmium sulfide (CdS) particles is investigated by means of static and dynamic fluorescence spectroscopies and atomic force microscopy (AFM). The apparent association constant between HPV and CdS can be obtained from the plot of the relative fluorescence quantum yields versus the reciprocal concentrations of CdS. The electron injection rate from excited HPV to the conduction band of CdS can also be calculated. Both the constant and the electron injection rate are related to the chain length of the alkoxy group on the connecting modules, leading to the conclusion that the modification of HPV at certain substitution sites can control the interaction between HPV and nanosized CdS particles. The CdS particles with different surface charge may result in significant changes of the apparent association constants, which shows that the electrostatic force probably plays a key rol...

The PL and EL properties of a novel light-emitting alternating copolymer composed of triphenylamine (TPA) and phenylene vinylene derivate (MEHPPV), that is, TPA-MEHPPV and its blend with PVK were demonstrated. A considerable enhancement of the EL intensity was observed by using the polymer blends as the emission layer in the organic light-emitting devices (OLEDs). The energy transfer process in the polymer blends was also discussed.

A novel self-assembled (SA) film of a functional dendritic molecule, hyperbranched conjugated poly(phenylene vinylene) (SPPV), is obtained through the covalent bond linkage on a hydrophilic substrate (e.g., mica). The self-assembling process of the film is investigated in detail by UV−vis and fluorescence spectroscopy, and the morphology of the films are observed by atomic force microscopy. Hyperbranched molecules require longer times for forming highly ordered and homogeneous molecular films (several days) compared to small molecules. Excimers formed from the excited state of SPPV in these SA films can be detected by their fluorescence properties. The difference of fluorescence properties between the SPPV SA film and spin-coating film shows that the SA film is ordered and homogeneous. Finally, the photovoltic response is reported for these SA films.

A novel light-emitting alternating copolymer, known as hyperbranched conjugated polymer (HPV), has been designed and synthesized by Wittig reaction, and so have its linear counterparts, including MPV and PPV. FTIR,1H NMR,13C NMR and GPC were combined to characterize these polymers. Their photophysical properties were investigated both in solution and in solid film. Interestingly, almost the same maxima of absorption and emission wavelengths were observed for the solution of HPV and MPV in CH2Cl2 respectively, located at the shorter wavelength region related to PPV. In addition, the absorption peak of HPV film blue shifted while its emission peak red shifted as MPV compared with the case of its CH2Cl2 solution. However, both the absorption and emission spectra of the PPV film showed red shift, which resulted from a special electronic structure.

In recent years, there is a worldwide interest in the area of organic electroluminescence (EL) stimulated by the promising application of light-emitting diodes for the fabrication of large, flexible, flat and inexpensive displays. This article provides a review based on a part of our research works including design and characterization of highly electron affinitive polymers, multi-functional EL material and organic-soluble rare earth metal complex. Their device performance using these materials as emissive layers is also involved.

The conjugated dendrimer, poly(3,5-bisvinylic)benzene (HS1), was synthesized by two routes. Elementary analysis, FTIR, NMR and GPC spectra were used to characterize the dendrimer. HS1 has good solubility in common organic solvents although it does not contain long alkyl side chain. The photophysical properties in solution and net solid film are inspected. Absorption maxima were determined at 290 and 310 nm with a molar absorption coefficient in the order of 104, and the emission maxima were at 359 and 369 nm. The excitation spectrum is similar to that of the absorption. A mirror image relationship existed between the absorption and emission spectra characteristic of the rigid structure of the polymer. The Stokes shift (70 nm) is large, which means the large difference in the energy level between the ground and singlet excited state. The fluorescence quantum yield is about 36%. The net film of HS1 has a broad emission at 446 nm. The marked difference between the solution and net solid film in photophysical properties suggested the large change in intermolecular interaction from solution to the solid film state. Molecular mechanical calculations are used to aid the design and simulation of the structure of HS1. In generation 1–2, the optimized geometry shows a relatively good planarity. While the torsion appeared at the interference of the branches in generation 3 and the optimized geometry feels a zeolite structure. The calculation result is used to explain the experimental observation. The good photophysical properties and processing ability could make HS1 an ideal candidate in electroluminecence device as a blue emitter.

A new class of novel high-efficiency light-emitting nitrogen-containing PPV-related copolymers which have hole transfer moieties such as triphenylamine (TPA) and alkyl-carbazole units and conjugated aromatic units such as 4,4′-biphenylene, 1,4-phenylene, 1,4- or 1,5-naphthylene and 9,10-anthrylene, was designed and synthesized by the well-known Wittig–Hornor reaction. The optical and electrical-properties were examined. The resulting alternating copolymers were highly soluble in common organic solvents, with good film-forming properties and high fluorescence quantum yields and also emit blue/green lights when used as the active layer of LEDs.

The photophysical properties of the first crown ether-bearing [60]fulleropyrrolidine (CFP) have been studied. The absorption and fluorescence spectra are hypsochromically shifted by metal ions complexation via intramolecular electron transfer which is confirmed by AMI computation. The third-order optical nonlinearity of CFP is measured by time-resolved degenerate four-wave-mixing experiment. The third-order optical susceptibility χ(3) of CFP is 8.97×10−14 esu. The nonlinear optical temporal response is second-order exponential, the fast process is determined as 120 ps.

A new type of novel high-efficiency light-emitting nitrogen-containing poly(phenylene vinylene) (PPV)-related copolymers, which have hole-transfer moieties such as triphenylamine (TPA) and conjugated aromatic units such as 4,4'-biphenylene, 1,4-phenylene, 2,5-dimethyl-1,4-phenylene, 1,4- or 1,5-naphthylene, and 9,10-anthrylene, was designed and synthesized by the well-known Wittig-Hornor reaction. The resulting alternating copolymers were highly soluble in common organic solvents. They can spin-cast onto various substrates to give highly transparent homogeneous thin films without heat treatment. The introduction of TPA units in the PPV backbone improved processibility and limited the π-conjugation length. Furthermore, the additional π-electron delocalization between the lone-paired electron in the nitrogen atom and π-electrons in the conjugated units contributed to the improvement of the fluorescence quantum yields of these copolymers. All these alternating copolymers except TPA-PAV have high-efficiency photoluminescence and they are very promising for light-emitting diodes (LEDs). It is very promising that TPA-PAV will emit white light when used in LED device due to the broad emission spectra. The origin of the broad spectrum is contributed by the charge-transfer complex formation, which can be proved by the absorption and emission spectra of TPA-PAV solutions. When the aromatic units were 1,4-phenylene, 1,4- or 1,5-naphthylene, 4,4'-biphenylene, and 9,10-anthrylene, respectively, with increase of the capability to accept electrons in aromatic units, the charge transfer from TPA to aromatic units occurred; consequently, the fluorescence quantum yield decreased. The introduction of the alkoxy-substitute group on the aromatic units in the polymer backbone caused the red shift of the absorption and emission spectra of the copolymers due to the stronger delocalization of the «-conjugated system.

Four dialkoxy-substituted poly(1,4-phenylenevinylene) (PPVs) and four copolymers of poly[(2-methoxy-5-(2′-ethylhexloxy)-p-phenylene vinylene)] (MEH-PPV) and non-substituted PPV were synthesized. The comparative photoluminescence properties of the resulting polymers are reported. In dilute solution the length of side chains plays an important role in the emission of PPVs, but the morphology of the films has an important effect on the photoluminescence. As for the four copolymers, the absorption and emission spectra were blue shifted and the fluorescence quantum efficiency improved with the increase of the non-substituted PPV content. These copolymers possess both the good solubility of MEH-PPV and the high fluorescence efficiency of PPV. Additionally, the chemical structures of these copolymers can be controlled. The emission of the copolymer films changed with the thickness of the films, which may be caused by the interaction between the two different chains of MEH-PPV and PPV on the copolymer backbone. The most important is that a laser-like emission was observed from MEH-PPV neat film, which suggested that PPVs would be very promising laser materials. Copyright © 1999 John Wiley & Sons, Ltd.