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 electrolumine...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.展开更多
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 ...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.展开更多
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 micro...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.展开更多
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,...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).展开更多
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 fr...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.展开更多
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 th...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.展开更多
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 fi...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.展开更多
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 a...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.展开更多
Stable monolayers of electropolymerized poly-N-vinylcarbazole (EPVK)and arachidic acid(AA) are obtained on a subphase of alkaline Tl2O3 colloidal solutions.As revealed by the atomic force microscope,there is phase sep...Stable monolayers of electropolymerized poly-N-vinylcarbazole (EPVK)and arachidic acid(AA) are obtained on a subphase of alkaline Tl2O3 colloidal solutions.As revealed by the atomic force microscope,there is phase separation in the mixed LB monolayers.Transmission electron microscopic observations reveal that oredred arrays of composite Tl2O3/Epvk nanowires are formed in the mixed monolayers.Formation of the composite nanowire arrays is attributed to the ordered adsorption of Tl2O3 colloidal particles along the polycationic EPVK chains.The composite nanowire array is 3.2nm wide with a spacing of 2.7nm.The composite nanowire arrays can also,be formed when pure EPVK is used.composite LB multilayers of Tl2O3/EPVK nanowire arrays are prepared.The bilayer spacing is 5054nm.The present study is of importance to the fabrication of inorganic semiconductor/functional polymer composite nanowires.展开更多
基金This work was supported by the National Natural Science Foundation of China(No.59790050-08)and the Youth Foundation of Tsinghua University.
文摘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.
基金Financial support for this word was given by the National Natural Science Foundation of China,Grant No:29774039
文摘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.
基金Project 29774039 was supported by the National Natural Science Foundation of China
文摘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.
文摘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).
基金This work was supported by the National Natural Science Foundation (Grant no. 59873001)
文摘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.
基金Financial Support by the National Science Foundation of China,Grant No.:29774039
文摘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.
文摘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.
基金supported by the National Natural Science Foundation of China(Nos.22105099 and 61874053)Natural Science Foundation of Jiangsu Province(No.BK20200700)+2 种基金the China Postdoctoral Science Foundation(No.2022M711591)the open research fund from Anhui Province Key Laboratory of Optoelectronic Materials Science and Technology(No.OMST202101)the State Key Laboratory of Luminescent Materials and Devices(South China University of Technology).
文摘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.
文摘Stable monolayers of electropolymerized poly-N-vinylcarbazole (EPVK)and arachidic acid(AA) are obtained on a subphase of alkaline Tl2O3 colloidal solutions.As revealed by the atomic force microscope,there is phase separation in the mixed LB monolayers.Transmission electron microscopic observations reveal that oredred arrays of composite Tl2O3/Epvk nanowires are formed in the mixed monolayers.Formation of the composite nanowire arrays is attributed to the ordered adsorption of Tl2O3 colloidal particles along the polycationic EPVK chains.The composite nanowire array is 3.2nm wide with a spacing of 2.7nm.The composite nanowire arrays can also,be formed when pure EPVK is used.composite LB multilayers of Tl2O3/EPVK nanowire arrays are prepared.The bilayer spacing is 5054nm.The present study is of importance to the fabrication of inorganic semiconductor/functional polymer composite nanowires.
