EMISSION CHARACTERISTICS OF ORGANIC LIGHT-EMITTING DIODES WITH A HETEROSTRUCTURE OF DYE DOPED POLY(N-VINYLCARBAZOLE)/TRIS(8-HYDROXYQUINOLINE) ALUMINUM

Organic electroluminescent diodes with a heterostructure of 9,10-bis(phenylethnyl) anthracene (BPEA) doped poly(N-vinylcarbazole) (PVK)/tris(8-hydroxyquinoline)aluminum (Alq(3)) have been fabricated. The electroluminescence (EL) both from BPEA and Alq(3) were observed when the Alq(3) layer is thin enough. With increasing thickness of the Alq(3) layer, the relative emission intensity of BPEA is gradually decreased. For the thin Alq(3) layer structure, the light emission of Alq(3) becomes more dominant as the applied voltage increases. It is proposed that the electron-hole recombination takes place in both PVK and Alq(3) films. The field-induced quenching theory has also been applied to explain the change of the EL spectra with applied voltage.

SYNTHESIS OF OPTICALLY ACTIVE POLY (N-VINYLCARBAZOLE)S

The organic salts as initiators [A*B-+(-):Ph*3C+ClO4-, Ph(3)*C+SbCl6-, (-)Sp*(ClO4-)-Cl-+ and (-)(Sp)(2)*(+3)(ClO4-)(3)] and catalysts [A(+)B*(-):(+)CSA*, A*B-+*(-):Ph(3)*C+(+)CSA*(-) and (-)Sp*(+)(+)CSA*] are prepared and characterized by specific rotation. The asymmetrically stereoselective induction of the initiators and catalysts in thc polymerization of N-vinylcarbazole is in an order of A*B-+*(-) > A(+)B*(-) > A*B-+(-). The specific rotations of obtained poly(N-vinylcarbazole) (PVCZ) generally are in accordance with mentioned order.

POLYMERIZATION MECHANISM OF N-VINYLCARBAZOLE WITH CHIRALLY ORGANIC SALT AS CATALYST

The polymerization mechanism is described by the conductance change with the time during the polymerization. The mechanism can be explained by the equilibrium feature (i.e. main ion-pairs) between the free ions and the ion-pairs dissociated by the organic salt (-) Sp*(+)(+) CSA*(-) (An asterisk represents the chirality) and the scheme of the polymerization process is described mainly by the charge transfer complexes having chiral induction power.

The Storage Cell Circuit with Memristor Characteristics of Poly(N-Vinylcarbazole) Films

A kind of non-conjugated polymer memory material, poly（N-vinylcarbazole）, is used to investigate silicon-based storage performance with the fact that the one-bit storage cell circuit consists of a sandwiched indium-tin- oxide/poly（N-vinylcarbazole）/Al and an n-type metal-oxide-semiconductor field effect transistor. The memristor on the basis of a nano poly（N-vinylcarbazole） film exhibits electrical bistability and flash memory features, for which the switching-on voltage is -1 V and the on/off current ratio approaches 104. At ambient temperature, the memory circuit possesses higher reliability within the programming time 104 s. The output voltage is dose to 0.5 V during logic 1, while it is approximately 14mV in the logic 0. This paves the way for the study on the technology concerning the binary encoding and data storage of nonvolatile memories.

Photorefractive Effect in Poly(N-vinylcarbazole)-Based Composite Sensitised by C_(60)

A new PVK-based photorefractive polymer composite sensitized by C60 and doped with a higher content of EO chromophore was prepared. The high optical quality thin-film was formed between two ITOcovered glass electrodes. Two-beam-coupling (2BC) experiment was performed by using a He-Ne laser (at wavelength 632.8nm), and an obvious photorefractive performance was observed. The dependence of two-beamcoupling gain coefficient on the applied poling dc electric field was measured.

MORPHOLOGICAL CHARACTERIZATION OF POLY (N-VINYLCARBAZOLE) OBTAINED WITH ASYMMETRICALLY STEREOSELECTIVE POLYMERIZATION

The morphological characterizations of poly(N-vinylcarbazole)(PVCZ) obtained by asymmetrically stereoselective polymerization were studied using x-ray diffraction pattern, DSC and GPC. The results show that the PVCZs have lower crystallinities (11.0 similar to 18.6%) and lower melting heats (2.2 similar to 7.5 J/g), but the degree of crystallinities of the PVCZ samples obtained using the organic salts (acid) with chiral or stereodifferentiating ligands are higher than that using radical and general protonic initiator. It has shown that the crystallization is directly related to the packing density of the hexagonal array of the rodlike molecules formed from the helical chain.

STRUCTURE AND PROPERTIES OF POLY (N-VINYLCARBAZOLE) OBTAINED VIA ASYMMETRICALLY STEREOSELECTIVE POLYMERIZATION

The structure and properties of poly(N-vinylcarbazole) (PVCZ) obtained via asymmetrically stereoselective polymerization have been studied by using **1H NMR spectra, UV spectra, DSC analysis and GPC. The steric microstructure i.e. the content of isotactic sequences was found to be increased by using AIBN to ( minus )Sp***** plus ( plus )CSA***** minus as the initiators or catalysts and the mole extinction coefficient to be decreased. Bimodal molecular weight distribution (MWD)s of the obtained PVCZs were caused by two propagating species of the free ions and the ion-pairs associated with the organic salts during polymerization. (Author abstract) 19 Refs.

Fluorescence Spectra of the Poly (N-vinylcarbazole)Obtained with Asymmetric Polymerization

The fluorescence spectra of the poly (N-vinylcarbazole) in solution obtained with chirally organic salts or acid as catalyst or initiator [ (-)Sp: (-)-Sparteine, (+)CSA: D- (+)Camphor-10-sulfonic acid)], respectively, have been investigated. It is found that the two emission peaks at the longer wavelength (lambda max, ca, 415nm) and the shorter wavelength (lambda max, ca, 370nm) are assigned to the sandwich excimer and second excimer (partial overlap) fluorescence, respectively. The sandwich excimer and partially overlapped excimer are attributed to a fully overlapped structure of neighbouring carbazole chromophores in a totally elipsed conformation of the isotactic sequence, and partially overlapped structure of the syndiotactic sequence. The estimated values of I-415/I-370 and isotactic sequence content by using the fluorescence spectra are in the order: (-)Sp(+) (+)CSA(-)> (+)CSA(-)> (-)Sp(+)ClO(4)(-) (no peak at 415nm for AIBN).

Green Light-Emitting Organic Electroluminescent Device with a New Fluorescent Dye Dispersed in Poly(N-vinylcarbazole) Emitter Layer

Double-layer organic electroluminescent devices have been constructed. A new fluorescent dye, 9,10-bis(phenylethynyl)anthracence, was chosen as the dopant which was molecularly dispersed in the polymer film, and green light was observed from the device with luminance of 130cd/m(2) at 17V.

STUDY ON LIQUID CRYSTALLINITY OF POLY(N-VINYLCARBAZOLE)

The liquid crystallinity of poly(N-vinylcarbazole) was studied by using powder X-ray diffraction, polarized opticalmicroscopy, and differential scanning calorimetry. The results show that the lower molecular weight fractions of this polymerdo not form a liquid crystalline phase, while the samples of sufficiently high molecular weight do form a mesophase attemperatures above the glass transition. The lowest value of the degree of polymerization for PVK to form a stable liquidcrystalline phase was found to be in the range of 150 to 200, significantly higher than the value of 50 for most conventionalside chain liquid crystaline polymers.

Thermally Induced Nanocrystal Array of Poly(N-Vinylcarbazole) on Si-Wafer Substrate

Recently, nanostructures such as nanocrystals and nanoaggregates have attracted much attention in many quarters of materials, electronics, and biology to create higher-value-added functional nanoscale materials and films. In this research, the fabrication of nanoaggregates on ultrathin photoconductive films of poly(N-vinylcarbazole) (PVCz) by applying thermal treatment is demonstrated. The structure and size are discussed on the basis of the results of atomic force microscope images. As a result, after thermal treatment of these films above the glass transition temperature (Tg) of PVCz, different types of surface morphological changes were induced showing a dependence on the tacticity of PVCz. Radically polymerized PVCz(r) ultrathin film showed small aggregates with heights of ~8 nm on the film surface after thermal treatment, while cationically polymerized PVCz(c), which has higher isotactic diad fractions than PVCz(r), indicated similar aggregates on the film surface, although the number of aggregates was smaller than PVCz(r). It is considered that these different phenomena depend on the tacticity of PVCz and the interaction between PVCz molecules and the substrate surface.

Asymmetric Polymerization of N-Vinylcarbazole with Optically Active Anionic Initiators

The anionic polymerization of N-vinylcarbazole（NVC） by using optically active anionic initiators such as the lithium salts of（S）-1-（9H-fluoren-2-yl）-4-isopropyl-4,5-dihydrooxazole（（S）-1-FIDH） and（S）-2-（9H-fluoren-2-yl）-4-isopropyl-4,5-dihydrooxazole（（S）-2-FIDH） and complexes of（-）-Sparteine with n-butylithium（n-Bu Li-（-）-Sp） or fluorenyl lithium（FILi-（-）-Sp） was achieved. The yield and specific rotation of poly（N-vinylcarbazole）s（poly（NVC）s） were considerably affected by the molar ratio of（S）-FIDH to NVC. The highest yield and specific rotation were obtained with Li-（S）-1-FIDH as an initiator, with a molar ratio of monomer and initiator [M]/[I] = 10/1. The effects of the chiral initiators, type of solvent and the polymerization temperature were investigated. The obtained optical activity of polymers was attributed to asymmetric induction of the chiral initiators.

THE CATALYTIC EFFECTS OF OXYGEN AND AMINES IN THE REDOX-INITIATED DIMERIZATION OF N-VINYLCARBAZOLE*

The redox reaction between N-vinylcarbazole (NVC) and various oxidants including Ce(Ⅳ), Fe(Ⅲ)and benzoylperoxide in methanol proceeds via the initial formation of the NVC N-cation radical which in turn leads to the formation of the NVC cyclic dimer, trans-1,2-dicarbazylcyclobutane. Molecular oxygen and a few arylamines are able to accelerate the rate of the formation and increase the yield of the dimer. The mechanism of this process and the functions of oxygen and arylamines are presented as follows: The participation of molecular oxygen is to facilitate the dissociation of the resulting reduced metal ion and the NVC N-cation radical ion pair or charge transfer complex, thereby releasing the free NVC N-cation radical and increase the rate of the formation and yield of the dimer. The arylamine in this reaction between NVC and oxidants can be viewed as electron transfer agent between NVC and the oxidant. Because the amines are present in small amount relative to the oxidants and can be regenerated in process, it is essentially catalytic in nature.

Fluorene pendant-functionalization of poly(N-vinylcarbazole)as deep-blue fluorescent and host materials for polymer light-emitting diodes

π-Electron coupling of pendant conjugated segment inπ-stacked semiconducting polymers always causes the formation of defect trapped sites and further quenched high-band excitons,which is harmful to the performance and stability of deep-blue polymer light-emitting diodes(PLEDs).Herein,considerate of“defect”carbazole(Cz)electromers in poly(N-vinylcarbazole)(PVK),a series of fluorene units are introduced into pendant segments(PVCz-DMeF,PVCz-FMeNPh and PVCz-DFMeNPh)to suppress the strongπ-electron coupling of pendant Cz units and enhance radiative transition toward fabricating sable PLEDs.Compared to PVCz-FMeNPh and PVCz-DFMeNPh,PVCz-DMeF spin-coated films show a relatively efficient deep-blue emission,completely similar to its single pendant chromophore,confirmed an extremely weak charge-transfer and electron coupling between adjacent pendant segments.Therefore,PLEDs based on PVCz-DMeF present stable and deep-blue emission with a high color purity(0.17,0.08),associated with extremely weak defect emission at 600∼700nm(induced by carbazole electromers).Finally,PLEDs based on PVCz-DMeF/F8BT blended films(1:1)also present the high maximum luminance(Lmax)of 6261 cd/m2 and current efficiency(CE_(max))of 2.03 cd/A,confirmed slightly trapped sites formation.Therefore,precisely control the arrangement and packing model of pendant units inπ-stacked polymer is an essential prerequisite for building efficient and stable emitter for optoelectronic devices.

One Pot Synthesis of Medicinally Important cis-2.Methyl-4-am i no s u bstituted-1,2,3,4-tetrahyd roq u i nolines

A simple synthesis of medicinally important cis-2-methyl-4-azapan-2-one-1,2,3,4-tetrahydroquinolines/cis-9- （2-methyl-l,2,3,4-tetrahydroquinolin-4-yl）-9H-carbazole was reported. Multicomponent one pot synthesis with ani- lines and N-vinylcaprolactam/N-vinyl carbazole via imino Diels-Alder reaction by using antimony trichloride as catalyst and acetonitrile as solvent was employed. NMR technique （2D） was used to study the regio- and stereo- chemistry of newly synthesized compounds. The cis diastereo-selectivity of the products was predicted by COSY and NOESY studies.