Solution processible naphthalene and perylene bisimides: Synthesis,electrochemical characterization and application to organic field effect transistors (OFETs) fabrication

A series of alkyl- or alkylphenyl-1,4,5,8-naphthalenetetracarboxylic-1,4:5,8-bisimides together with the comparative series of the corresponding 3,4,9,10-perylenetetracarboxylic-3,4:9,10-bisimides have been synthesized and characterized by cyclic voltammetry. The naphthalene bisimides family shows a clear dependence of its first reduction potential – corresponding to the LUMO level – on the nature of the N-substituent. Naphthalene bisimides containing alkylphenyl groups undergo the first 1e reduction at potentials of ca. 100 mV higher than those with alkyl groups (ca. −900 mV vs ca. −1000 mV with respect to Fc/Fc⁺ couple). No effect of the nature of the substituent is observed for the corresponding perylene bisimide series. Due to their improved solution processibility the synthesized organic semiconductors can be used for the fabrication of all organic, flexible n-channel field effect transistors (OFETs) through spin coating and printing techniques, without the necessity of the use of vacuum deposition techniques. The best of the fabricated transistors, operating in air show the charge carriers mobility of 4 × 10⁻² cm²/(V s) and the ON/OFF ratio equal to 4.5 × 10⁵.     

Synthesis of solution processable ultraviolet sensitive organic molecules and their application in hybrid UV photodetector

Two new solution processable organic molecules based on carbazole and triphenylamine (TPA) substituted fluorene were synthesized by Suzuki coupling reaction. The bandgap of the molecules can be controlled by the 3,6-linkage of the carbazole. The propeller-shaped TPA moieties endow the molecules with good thermal stability and perfect solution processability. Smooth films of both molecules could be readily obtained by spin-coating and n-type ZnO nanoparticles were further incorporated to construct bulk-heterojunction. Under the excitation of 1 mW/cm² ultraviolet light at 365 nm, devices with those hybrid films as active layers show a relative quick response with photo-to-dark current ratio of about three orders of magnitude. The current decay time (decay to 1% of the value before removing of the light) is less than 200 ms. Moreover, the spectral response of the devices covers 300–400 nm and can be well tuned by the conjugation length of the organic molecules. Those results indicate that the synthesized molecules might be candidates for solution processable low cost UV photodetectors.     

Syntheses and properties of cyano and dicyanovinyl-substituted oligomers as organic semiconductors

Thiophene-phenylene co-oligomers with cyano and dicyanovinyl substituents at different positions were synthesized. Their stability and energy levels were estimated through thermal gravimetric analysis, UV–vis absorption spectra and electrochemistry. Interestingly, the absorption of BTCV covered the range of 430–610 nm, and thin film transistors of BTCV exhibited p-type behavior with high stability, suggesting BTCV a good candidate for solar cell.     

Conducting organic polymers with electroactive dopants. Synthesis and electrochemical properties of hexacyanoferrate-doped polypyrrole

A systematic study of the synthesis of heacyanoferrate-doped polypyrrole (PPy/HCF) is reported. In addition to the electrochemical growth of films, we report three different modifications of a novel chemical synthesis for the preparation of bulk powdered materials by oxidative polymerization of pyrrole by the acid derivative of HCF. The effect of temperature and duration of the reaction, doping level and aging of the materials obtained on their conductivity has been systematically studied. Higher conductivities are obtained for materials prepared at lower temperatures (0°C). This is associated to a higher content of the doping HCF anion for these lower temperature materials. With time the conductivity of all samples decreases proportionally to the corresponding initial values. Finally, we report the electrochemical properties of these hybrid materials, the cyclic voltammograms of chemical and electrochemical derivatives and their intercalation behavior, which shows a deintercalation of the electroactive HCF anion in aqueous electrolytes but not in organic (propylene carbonate, dimethoxyethane) media.     

Synthesis and hole-transporting properties of vinyl-type polynorbornenes with ethyl ester linked triarylamine side groups

Palladium(II)-catalyzed polymerization of norbornene monomers bearing triarylamine side groups was investigated to prepare the vinyl-type polynorbornenes having hole-transporting properties. Norbornene monomers (M1–M3) with the ethyl ester linked aryldiphenylamines where the aryl group is phenyl, m-tolyl, and 1-naphthyl, respectively, were employed. The combined use of the Pd(II) catalyst supported by N-heterocyclic carbene ligand and AgSbF₆ leads to the production of soluble polynorbornenes (P1–P3). While the cyclic voltammetry measurements show the relatively low oxidational stability of polymers, the polymers exhibit the high glass transition temperature of 305–333 °C. The atomic force microscopy images of the thin film of P1 reveal the very smooth film surface with a roughness of 0.29 nm, indicating the good film-forming capability of polymer. When incorporated as a hole-transporting layer in Alq₃-based electroluminescent devices, the spin-coated polymer films display hole-transporting property suitable for the proper green emission of Alq₃. Among the devices studied, the one based on 1-naphthylamine-containing P3 exhibits the highest performance in terms of luminance and external quantum efficiency.     

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

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

New 1,3,4-oxadiazole containing materials with the effective leading substituents: The electrochemical properties,optical absorptions,and the electronic structures

The electrochemical and optical absorption properties as well as the thermal stabilities of a series of 1,3,4-oxadiazole dimers 1,3-bis[2-(4-methylphenyl)-1,3,4-oxadiazol-5-yl]benzene (OXD-X) and its derivatives with the different alkoxy substituents on the central benzene ring such as O(CH₂)_n−1CH₃ (OXD-An, n = 3, 7, 10, 16), O(CH₂)_nOC₆H₅CH₃ (OXD-Bn, n = 6), and O(CH₂)_nOC₆H₄NNC₆H₄OCH₃ (OXD-Cn, n = 3, 6, 10) are studied. The DSC measurements exhibit dramatically elevated glass transition temperatures for OXD-X and OXD-An (120–245 °C) in contrast to the well-known PBD (∼60 °C), indicating the better thermal stabilities. From OXD-X to OXD-An, OXD-Bn or OXD-Cn, the cyclic voltammograms and UV–vis absorption spectroscopy display significant variation, in which the later three species show additional lower energy absorptions at λ > 330 nm compared with OXD-X and particularly, both of OXD-Bn and OXD-Cn display an oxidation peak at ∼+1.0 V and two successive redox reactions occur for OXD-Cn. Theoretically, the B3LYP/6-31g calculations explore that these extraordinary properties are due to the influence of the substituents on the benzene ring to the frontier molecular orbital distribution, especially the O(CH₂)_nOC₆H₄NNC₆H₄OCH₃ groups in OXD-Cn deduce the new pictures of the frontier molecular orbitals, causing the electron-transporting behavior originally happening on the molecular skeleton transferred to the side chain.     

Synthesis,spectroscopic and magnetic properties of m–p aniline tetramers

Alternating m–p-N-hexylaniline and aniline tetramers have been synthesized via palladium-catalyzed amination reactions. The tetramers can be oxidized with m-chloroperbenzoic acid or NOBF₄ and form radical cations stable in acidic media. The magnetization measurements of oxidized N-hexylaniline or p-aniline tetramers reveal the paramagnetic-type behaviour.     

Synthesis and electrochemical properties of a new class of boron-containing n-type conjugated polymers

Several electron-deficient polymers containing the 9,10-diboroanthracene unit have been synthesized and characterized. Electrochemical study shows that they have high electron affinities. Photoluminescence of rr-P3HT is quenched in the presence of one of the polymers in the solid state, demonstrating the potential utility of this class of polymer as powerful n-type materials in organic photovoltaic devices.     

Magnetoresistance for organic semiconductors: Small molecule,oligomer, conjugated polymer,and non-conjugated polymer

Organic semiconductor (OSC) devices have been shown to have a large magnetoresistance (MR) response at room temperature for relatively small-applied magnetic fields of 0.1–100 milli-Tesla (mT). This large MR is not limited to one class of organics, but is seen in small molecules, oligomers, conjugated polymers, and non-conjugated polymers. In this paper, data is presented on the MR effect for the poly(phenylene vinylene) (PPV) derivative “Super Yellow,” for poly(vinylenecarbazole) (PVK), for alpha-sexithiophene (α-6T), and for tris(8-hydroxyquinoline) aluminum (Alq₃). The data is analyzed in the context of the Magnetoresistance by the Interconversion of Singlets and Triplets (MIST) model. The MR data of Alq₃ for magnetic fields of less than 1 mT are fitted to a polynomial expansion, and an estimate for the hyperfine interaction constant, which is consistent with values for small molecules, is extracted from the fitting parameters. Curve fits at fields in the 100 mT range are also presented and they show that there exist two kinds of magnetic field behavior, inverse square root, and inverse even orders. Furthermore, the scaling factor at this range is one order of magnitude larger than that found in the 3 mT range.     

A structural,electronic and electrochemical study of polypyrrole as a function of oxidation state

The electronic, structural, and chemical properties of polypyrrole doped with the hexafluorophosphate ion are investigated as a function of oxidation state. These properties are found to be highly correlated; specifically, they all experience a rapid transition at approximately −0.1 V versus SCE. The electronic conductivity of the film changes by two orders of magnitude through the transition potential, in the well-known doping-induced metal–insulator transition. Also at −0.1 V versus SCE, X-ray diffraction and macroscopic actuation measurements reveal a structural change in the polymer. Results suggest a loss of pi-stacking in the polymer crystals, and a reordering of the dopant ions in the matrix. The dopants appear to exist in an isotropic liquid-like state in the highly oxidized film, changing to a channel structure at the transition point. This change in structure is also consistent with the transition observed in the electrochemical impedance spectrum. The equilibrium charge on the polymer with oxidation state is consistent with a constant DC capacitance, however the AC impedance spectrum shows increased constant phase element behavior in the reduced state. This could be due to a greater range of diffusion constants in the reduced state, which we associate with the heterogeneous ion configuration.     

Effect of donor moiety in organic sensitizer on spectral response,electrochemical and photovoltaic properties

This paper describes the effects of donating ability in a D (donor)–π–A (acceptor) structured organic dye on the HOMO and LUMO energy levels and photovoltaic performance in dye-sensitized solar cell. Two different dyes were synthesized based on the cyanoacetic acid as an acceptor and the phenyl-thiophene as a π-conjugated bridge, where one contains a diethyl amino group (P2) and the other has an ethoxy group (P5) as the donor. The HOMO–LUMO energy gap was significantly influenced by donor group, where change of ethoxy donor with stronger amino one in donating ability decreased the energy gap from 2.84 eV to 2.21 eV. Moreover, it was also found that HOMO energy level was more sensitive to change in donor group than LUMO one. Photovoltaic performances of P2- and P5-dye-sensitized solar cells were systematically investigated in terms of the effects of co-adsorbent concentration, TiO₂ film thickness and TiCl₄ post-treatment. Under the best condition, the P5 dye showed the conversion efficiency of 2.62%, while the P2 dye exhibited much higher efficiency of 5.89% due to broader absorption.     

锂蓄电池正极材料LiV3O8的合成和充放电性能

采用一种液相反应的方法合成LiV3O8化合物 ,首先由NH3·H2 O ,LiOH与V2 O5反应合成含有Li和V的反应前驱产物 ,然后在 180℃的真空环境中进行干燥处理 ,最后将此物质在 5 80℃温度下煅烧成最终产物。采用热重分析试验分析了反应的机理。X射线衍射结果显示得到的物质与用传统合成方法得到的LiV3O8化合物的结构相比 ,在 (10 0 )方向上的衍射峰强度降低很多。在室温、恒电流为 3A/m2 条件下进行充放电试验 ,在 1.8～4.0V范围内 ,首次放电容量达到 2 30Ah/kg ,15周后仍能达到 2 10Ah/kg。     

Thiazole-based polymers: Synthesis,characterization and electronic structure

We report on the preparation and characterization of conjugated polymers based on the thiazole ring: polythiazole and polythiazolothiazole. Our aim is to help in clarifying the role of the heteroatom in the conduction pathway by inserting nitrogen atoms within the polythiophene backbone. We also discuss the results of Valence Effective Hamiltonian calculations on two stereoregular models of polythiazole.     

New organic semiconductors for thin-film transistors: Synthesis,characterization, and performance of 4H-indeno[1,2-b]thiophene derivatives

Three new hybrid polycyclic aromatic 4H-indeno[1,2-b]thiophene derivatives (DIT-nT) were readily synthesized and characterized. Ultraviolet photoelectron spectroscopy (UPS) and inverse photoemission spectroscopy (IPES) study shows that the gap energies of these oligothiophene derivatives are dependent on the effective π-conjugation length of the molecules, with decreasing gap energies while the conjugated length is increased. More importantly, the hole injection barrier obtained from UPS and IPES studies decreases significantly at the metal-organic interface as the effective π-conjugation length of the molecules increases. Hence, the hole injection into DIT-2T is expected to be more facile than that into DIT-0T due to the smaller barrier. X-ray diffraction examination revealed that thin films are highly ordered, with the long axes of the molecules nearly perpendicular to the surface. The field-effect transistor (FET) devices based on the three oligomers show good p-type performance with high hole mobilities, and the highest value (0.014 cm² V⁻¹ s⁻¹) was obtained for the longest oligomer DIT-2T.     

Synthesis,characterization, and properties of a new thiophene–benzobisthiazole copolymer

Stille coupling reaction of 4,8-dibromo-2,6-dihexyl-benzo[1,2-d:4,5-d′]bisthiazole and 2,5-bis(trimethylstannyl)thiophene afford a new conjugated conducting copolymer 1. The polymer was completely soluble in common organic solvents. The electrical conductivity of the polymer is at about 3.8 × 10⁻¹ S/cm. The UV–vis spectra of the polymer in a chloroform solution and in a spin-cast film on a piece of glass show π–π^* absorption bands (λ_max) of 460 nm and 538 nm, respectively. The 78 nm red shift of the λ_max of the polymer in the film, in comparison to that observed for the polymer in chloroform, possibly indicates much more planarization and aggregates formation due to the π electron stacking in terms of inter-chain characteristics in the solid state. The structure of the polymer has been compared with that of compound 3 as model compound. Rationalizations are presented for optical properties of the polymer in relation to polymer structure.     

Stable blue-emitting molecular material derived from calix[4]arene and pyrazoline: Synthesis, optical and electrochemical properties

A novel blue-emitting molecular material derived from calix[4]arene and pyrazoline was designed and synthesized. Its photophysical properties were investigated in CHCl₃ solution and solid film by UV–vis and photoluminescent (PL) spectra. The maximum peaks are almost at the same positions both in UV–vis and PL spectra indicated that the grafted pyrazoline on calix[4]arene by chemical bond can help to disperse emitting pyrazoline chromophores in host material of calix[4]arene and tend to reduce the interaction of each pyrazoline molecule. Light-emitting diodes (LEDs) using this material as active layer were fabricated by a wet process. The turn-on voltage of the typical LED based on calix[4]arene-pyrazoline was about 6.6 V, and the maximum EL efficiency of the device was determined to be 1.52%. The homogeneous film based the resulting material was obtained even after keeping for three months. The primary results indicate that this novel material is a promising candidate as pure blue and stable light-emitting material for display.