The synthesis and characterization of C60 chemically modified poly(N-vinylcarbazole)

Addition of C₆₀ moiety, a powerful electron acceptor to poly(N-vinylcarbazole) (PVK) by chemical reaction modifies considerably the physical and chemical properties of PVK. The characterization techniques employed are UV-visible, IR, DSC, TGA, ESR, ¹³C-NMR spectroscopy, scanning electron microscopy, XRD, and cyclic voltammetry. The fullerenated PVK, which has a visibly earthy yellow cast when compared with the unreacted polymer, has a new structure in the UV-vis absorption spectrum with the active range extending from about 280 to 870 nm, its apparent temperature sensitivity is intriguing, and an unusual temperature dependence for the ESR spectrum is observed. Considerable difference of electronic structure between pure PVK and C₆₀-PVK copolymer is indicated. The thermal stability and oxidation-reduction activation of pure PVK are enhanced by C₆₀-chemical modification. © 1996 John Wiley & Sons, Inc.     

Transient Absorption Spectral characterization of Electron Transfer between Fullerenes（C60／C70）and N,N,N’，N’—Tetra（p—methylphenyl）—4,4’—diamino—1,1’—diphenyl Sulphide（TPDAS）

In search of new systems with a photoexcited redox pair which exhibits a strong and stable photoinduced absorption band to understand the photophyscial and photochemical properties of electron transfer between fullernes (C60/C70) and organic donor[N,N,N’，N’-tetra(p-methylphenyl)-4,4’-diamino-1,1’-diphenyl sulphide(TPDAS)],we studied characteristic absorption spectra in the near-IR region obtained from 532nm nanosecond laser flash photolysis of a mixture of the fullerenes (C60/C70) and TPDAS in polar solvents.When fullerenes (C60/C70)were photoexcithed,the rise of the radical anion of fullerenes (C60/C70)with the rapid decay of their excited triplet states were observed in benzonitrile.It can be deduced that the electron transfer reaction does take place from TPDAS to excithed triplet state of rullerens(C60/C70).The rate consants(ket)and quantum yiekls(φet) of this process have been also evaluated.     

Photoinduced Electron Transfer between N,N, Nr,N' ‐Tetra‐(p‐methylphenyl)‐4, 4‐diamino‐1, 1'‐diphenyl Ether (TPDAE) and Fullerenes (C60/C70) by Laser Flash Photolysis

The photoinduced electron‐transfer reaction of N, N, N', N'‐tetra‐(p‐methylphenyl)‐4,4'‐diamino‐1,1'‐diphenyl ether (TPDAE) and fullerenes (C₆₀/C₇₀) by nanosecond laser flash photolysis occurred in benzonitrile. Transient absorption spectral measurements were carried out during 532 nm laser flash photolysis of a mixture of the fullerenes (C₆₀/C₇₀) and TPDAE. The electron transfer from the TPDAE to excited triplet state of the fullerenes (C₆₀/C₇₀) quantum yields and rate constants of electron transfer from TPDAE to excited triplet state of fullerenes (C₆₀/C₇₀) in benzonitrile have been evaluated by observing the transient absorption bands in the near‐IR region where the excited triplet state, radical anion of fullerenes (C₆₀/C₇₀) and radical cations of TPDAE are expected to appear.     

内含C60掺杂空穴传输层的量子点电致发光器件

聚乙烯咔唑（PVK）中掺入富勒烯（C₆₀）的重量比从0%到10%变化,以研究在空穴传输层中掺杂C₆₀后对量子点电致发光器件性能的影响。掺入C₆₀后的PVK薄膜在氧化铟锡（ITO）基底上均方根粗糙度从3nm降至1.6nm。另外,掺入C₆₀后有利于空穴的注入和传输,改善器件中电子和空穴的平衡,提高了器件的效率。     

内含C_(60)掺杂空穴传输层的量子点电致发光器件

聚乙烯咔唑(PVK)中掺入富勒烯(C60)的重量比从0%到10%变化,以研究在空穴传输层中掺杂C60后对量子点电致发光器件性能的影响。掺入C60后的PVK薄膜在氧化铟锡(ITO)基底上均方根粗糙度从3 nm降至1.6 nm。另外,掺入C60后有利于空穴的注入和传输,改善器件中电子和空穴的平衡,提高了器件的效率。     

Luminescence properties of epoxy resins modified with a carbazole derivative

Luminescence properties of a new material - epoxy resin with added 9-(2,3-epoxypropyl)carbazole (REPK) were studied. Absorption and photoluminescence (PL) spectra of REPK are compared with those of poly(N-vinylcarbazole) (PVK). PL in REPK is shifted to shorter wavelengths. Its intensity is higher than in PVK. REPK emits light in the range from 330 nm to 470 nm. PL spectrum of REPK could be well deconvoluted for four emission bands.     

Enhanced diffraction efficiency in a photorefractive liquid crystal cell with poly(9-vinylcarbazole)-infiltrated mesoporous TiO2 layers

The photorefractive effect of a layer-structured liquid crystal cell was significantly enhanced when a C60-doped poly(9-vinylcarbazole) (PVK)/TiO2 nanocomposite was used in two photoconductive layers. The C60-doped PVK/TiO2 nanocomposite film was prepared by infiltrating C60-doped PVK into a highly ordered mesoporous TiO2 layer. The addition of the TiO2 layer to the C60-doped PVK layer increased the first-order Raman-Nath diffraction efficiency from 24% to 42.9%. This enhancement of diffraction efficiency is attributed to a blocking effect of charge recombination in the composite layer. The electron transfer from the PVK layer into the TiO2 layer would decrease the recombination of photogenerated charges in the PVK layer, while charges in the PVK layer could participate in the formation of a space-charge field.     

Self-Assembly of Rod-Coil Block Copolymers for Photovoltaic Applications

Summary: Two different approaches to obtain electron donor-acceptor interfaces via self-assembly of block copolymer systems are discussed, where the donor domains are formed by a π-conjugated rod-like polymer and the acceptor domains result from a coiled polymer modified by C₆₀ fullerenes. In the first strategy, C₆₀ is chemically grafted onto the coil polymer, typically a statistical copolymer of styrene and chloromethyl styrene. This has as major effect the increase in molecular weight and volume fraction of the coil block, which can markedly perturb the self-assembled block copolymer final morphologies and eventually suppress any microseparated nanostructure in favour of fully isotropic homogeneous phases. We discuss how the presence of free homopolymer rods in the system can help recovering a microphase separated morphology suitable for photovoltaic applications. In the second approach we discuss the poly(diethylhexyl-p-phenylenevinylene-b-4-vinylpyridine) (PPV-P4VP) rod-coil block copolymer system and we argue how supramolecular interactions among P4VP and free C₆₀ can be exploited to blend rod-coil block copolymers and C₆₀ preserving the original lamellar phase.     

TOF-GISANS investigation of polymer infiltration in mesoporous TiO2 films for photovoltaic applications

The structure of porous TiO₂ films and TiO₂:poly(N-vinylcarbazole) (PVK) composite films is investigated with time-of-flight grazing incidence small-angle neutron scattering (TOF-GISANS). The TiO₂ films have been prepared by application of a sol–gel process with a diblock copolymer as structure directing agent, and the conductive polymer PVK is infiltrated in the porous network by spin coating and solution casting. The films show a hierarchical pore structure with mesopores 52 nm in size and additional large macropores with a diameter of about 180 nm. By matching the scattering contrast of the TiO₂ with the polymer information about the penetration of the polymer in the pores is determined. Whereas in the PVK film prepared by solution casting the pores are filled to a high degree; in the spin coated film, PVK wets only the TiO₂ pore walls and forms a solid overlying layer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1628–1635, 2010     

新型含铽共聚物的合成及其电致发光研究

将稀土金属Tb配合物单体与N-乙烯基咔唑（NVK）以及甲基丙烯酸甲酯（MMA）共聚, 合成了一种含Tb配合物的新型聚合物PKMTb, 并以红外光谱、紫外光谱表征了其光谱特性, 研究了其荧光特性和能量转移机制. 利用这种聚合物成功地制成了单层电致发光器件ITO/PKMTb/Al, 其具有半导体二极管的电流-电压特性, 在正相偏压下发绿光, 并探讨了其电致发光机理.     

Spectrophotometric studies of CT complexes of poly(N-vinylhalogenocarbazole)s with 2,4,7-trinitrofluorenone

The effect of chlorine, bromine, and iodine at the 3 and 3,6 positions on a carbazole ring with thermodynamic properties, that is, enthalpy, entropy, and a stability constant of CT complex poly(N-vinylcarbazole–2,4,7-trinitrofluorenone), were studied in a temperature range of 268–323 K. The discussion of the results obtained, based on linear free-energy relationships, stressed the advantageous influence of the halogen substituent in the carbazole ring on the properties of the poly(N-vinylcarbazole)–2,4,7-trinitrofluorenone complex.     

Triplet level-dependent photoluminescence and photoconduction properties of π-conjugated polymer thin films doped by iridium complexes

Triplet energy level-dependent decay pathways of excitons populated on iridium (Ir) complexes within π-conjugated polymeric matrices were studied by means of photoluminescence (PL) and photoconduction action spectroscopy. We chose a set of matrices, poly(9-vinylcarbazole) (PVK), poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (PF2/6), poly [2-(5′-cyano-5′-methyl-hexyloxy)-1,4-phenylene] (CNPPP), and poly [2-(5′-cyano-5′-methyl-hexyloxy)-1,4-phenylene-co-pridine] (CNPPP-py10 and CNPPP-Py20), having triplet energy levels ranging from 2.2 up to 3.0 eV. As Ir-complex dopants, we selected three phosphorescent emitters, iridium(III)bis(2-(2′-benzothienyl) pyridinato-N-acetylacetonate) (Ir(btp)₂acac), iridium(III)fac-tris(2-phenylpyridine) (Ir(ppy)₃), and iridium(III)bis[(4,6-fluorophenyl)-pyridinato-N,C^2′]picolinate (FIrpic), having triplet energy levels of 2.1, 2.5, and 2.7 eV, respectively. It was found that the triplet emission from the dopants, being populated via energy transfer from the matrices, was strongly dependent on the matching of triplet energy levels between matrix polymers and Ir-complexes. Photocurrent action spectra confirm effective exciton confinement at the dopants sites in the case of PVK matrix systems.     

A Supramolecular [10]CPP Junction Enables Efficient Electron Transfer in Modular Porphyrin–[10]CPP⊃Fullerene Complexes

Efficient photoinduced electron transfer was observed across a [10]cycloparaphenylene ([10]CPP) moiety that serves as a rigid non‐covalent bridge between a zinc porphyrin and a range of fullerenes. The preparation of iodo‐[10]CPP is the key to the synthesis of a porphyrin–[10]CPP conjugate, which binds C₆₀, C₇₀, (C₆₀)₂, and other fullerenes (K_A>10⁵ m ^?1). Fluorescence and pump–probe spectroscopy revealed intramolecular energy transfer between CPP and porphyrin and also efficient charge separation between porphyrin and fullerenes, affording up to 0.5 μs lifetime charge‐separated states. The advantage of this approach towards electron donor–acceptor dyads is evident in the case of dumbbell‐shaped (C₆₀)₂, which gave intricate charge‐transfer behavior in 1:1 and 2:1 complexes. These results suggest that [10]CPP and its cross‐coupled derivatives could act as supramolecular mediators of charge transport in organic electronic devices.     

Preparation of fluoride anion responsive poly(N-vinylcarbazole)-borane complexes

A series of novel fluoride anion responsive materials were facilely prepared by complex formation of poly(N-vinylcarbazole) with organoboron compounds in tetrahydrofuran. After addition of fluoride anion, visual color changes of fluorescence emission from green to blue were observed. The ¹¹B NMR spectra shown that poly(N-vinylcarbazole)-borane complexes were converted to poly(N-vinylcarbazole) and fluoroborate in the presence of fluoride anion. Among the obtained poly(N-vinylcarbazole)-borane complexes prepared, poly(N-vinylcarbazole)-triethylborane complex exhibited the most distinct visual changes in fluorescence emissions.     

Comparison of Operating Mechanisms for the Poly(N-vinylcarbazole) Based Non-Volatile Memory Devices

Summary: The organic non-volatile memory devices (NVMs) based on poly(N-vinylcarbazole) (PVK) with the different structures and compositions were fabricated and evaluated. The resistance states in the devices were controlled by the external electric field and exhibited the distinctive properties; the device with a single PVK layer was a write-once read-many-times memory by the field induced filament as a conduction path and its memory properties depended on the PVK thickness, the PVK/Al/PVK structured device was operated by a space charge limited current model and was sensitive to preparing condition of the internal Al layer, and the device performances with the PVK based charge transfer complex depended on the composition of the CT materials and the surface condition of the bottom electrode.     

Thermo‐responsive fluorescent micelles from amphiphilic A3B miktoarm star copolymers prepared via a combination of SET‐LRP and RAFT polymerization

A novel amphiphilic A₃B miktoarm star copolymer poly(N‐isopropylacrylamide)₃‐poly(N‐vinylcarbazole) ((PNIPAAM)₃(PVK)) was successfully synthesized by a combination of single‐electron transfer living radical polymerization (SET‐LRP) and reversible addition‐fragmentation chain transfer (RAFT) polymerization. First, the well‐defined three‐armed poly(N‐isopropylacrylamide) (PNIPAAM)₃ was prepared via SET‐LRP of N‐isopropylacrylamide in acetone at 25 °C using a tetrafunctional bromoxanthate iniferter (Xanthate‐Br₃) as the initiator and Cu(0)/PMDETA as a catalyst system. Secondly, the target amphiphilic A₃B miktoarm star copolymer ((PNIPAAM)₃(PVK)) was prepared via RAFT polymerization of N‐vinylcarbazole (NVC) employing (PNIPAAM)₃ as the macro‐RAFT agent. The architecture of the amphiphilic A₃B miktoarm star copolymers were characterized by GPC, ¹H‐NMR spectra. Furthermore, the fluorescence intensity of micelle increased with the temperature and had a good temperature reversibility, which was investigated by dynamic light scattering (DLS), fluorescent and UV‐vis spectra. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4268–4278, 2010     

Morphological transitions in aggregates of thermosensitive poly(ethylene oxide)‐b‐poly(N‐isopropylacrylamide) block copolymers prepared via RAFT polymerization

Double hydrophilic poly(ethylene oxide)‐b‐poly(N‐isopropylacrylamide) (PEO‐b‐PNIPAM) block copolymers were synthesized via reversible addition‐fragmentation chain transfer (RAFT) polymerization, using a PEO‐based chain transfer agent (PEO‐CTA). The molecular structures of the copolymers were designed to be asymmetric with a short PEO block and long PNIPAM blocks. Temperature‐induced aggregation behavior of the block copolymers in dilute aqueous solutions was systematically investigated by a combination of static and dynamic light scattering. The effects of copolymer composition, concentration (C_p), and heating rate on the size, aggregation number, and morphology of the aggregates formed at temperatures above the LCST were studied. In slow heating processes, the aggregates formed by the copolymer having the longest PNIPAM block, were found to have the same morphology (spherical “crew‐cut” micelles) within the full range of C_p. Nevertheless, for the copolymer having the shortest PNIPAM block, the morphology of the aggregates showed a great dependence on C_p. Elongation of the aggregates from spherical to ellipsoidal or even cylindrical was observed. Moreover, vesicles were observed at the highest C_p investigated. Fast heating leads to different characteristics of the aggregates, including lower sizes and aggregation numbers, higher densities, and different morphologies. Thermodynamic and kinetic mechanisms were proposed to interpret these observations, including the competition between PNIPAM intrachain collapse and interchain aggregation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4099–4110, 2009     

Synthesis of new nanocrystal-polymer nanocomposite as the electron acceptor in polymer bulk heterojunction solar cells

A hydroxyl-coated CdSe nanocrystal (CdSe-OH) and a CdSe-polymer nanocomposite were synthesized and used as the electron acceptors in polymer solar cells (PSCs). The CdSe-polymer composite was prepared via atom transfer radical polymerization (ATRP) of N-vinylcarbazole on functionalized CdSe quantum dots. Physical properties and photovoltaic characteristics of the CdSe-poly(N-vinylcarbazole) (CdSe-PVK) nanocomposite have been investigated. Thermogravimetric analysis (TGA) results displayed higher thermal stability for CdSe-PVK nanohybrid in comparison with the linear-type PVK polymer. Differential scanning calorimetry (DSC) studies indicated that CdSe-PVK had a lower glass-transition temperature (T_g) in comparison with PVK due to the branch effect of the star-shaped polymer hybrid. Cyclic voltammetric (CV) measurements were performed to obtain HOMO and LUMO values of PVK and CdSe-PVK. TEM and SEM micrographs exhibited CdSe nanoparticles were well coated with PVK polymer. Both CdSe-OH and CdSe-PVK were blended with poly(3-hexylthiophene) (P3HT) and used as the active layer in bulk heterojunction solar cells. Polymer solar cell based on CdSe-PVK as acceptor revealed that the photovoltaic properties can be significantly improved when PVK polymer chains were grafted on surfaces of CdSe nanocrystals. In comparison with the P3HT:CdSe-OH system, PSC based on P3HT:CdSe-PVK showed an improved power conversion efficiency (0.02% vs. 0.001%). Film topography studied by AFM further confirmed the better device performance was due to the enhanced compatibility between P3HT and CdSe-PVK.     

Electrochemiluminescence Studies of Phosphorescent Dopant and Host Molecules of Polymer Light-emitting Diodes

Electrochemiluminescence (ECL) from tris(2‐phenylpyridine)irdium [Ir(ppy)₃] was investigated following cross reaction of its anion with oxidized poly(N‐vinyl‐carbazole) (PVK) and its cation with reduced 2‐(4‐biphenylyl)‐5‐(4‐tert‐butyl‐phenyl)‐1,3,4‐oxadiazole (PBD). Both cross reactions show Ir(ppy)₃ emission and the cross reaction of PVK^+·/Ir(ppy)⁻₃ showed the highest ECL intensity. The comparisons of the reaction enthalpy and the energy of Ir(ppy)₃ light emitting shows that reaction between PVK^+· and Ir(ppy)⁻₃ is energy sufficient to populate metal‐to‐ligand charge transfer (MLCT) excited singlet (3.04 eV) of Ir(ppy)₃, while the reaction between Ir(ppy)⁺₃ and PBD^{− ·} is energy efficient to populate MLCT excited triplet (2.4 eV). The ECL result in solution reveals that the energy released from charge transfer between the Ir(ppy)₃ and PVK or PBD is sufficient to produce the excited state of Ir(ppy)₃ in solid polymer light‐emitting diodes (PLEDs) based on PVK:PBD hosts doped by Ir(ppy)₃. These results obtained will provide further insight into charge‐transfer excitation in PLEDs.     

Configurations conducive to the formation of intramolecular excimers in poly(N‐vinyl carbazole) and its copolymers

The ratios of the intensity of excimer and monomer emissions, denoted I_E/I_M, in poly(N‐vinyl carbazole) and copolymers of N‐vinyl carbazole and methyl methacrylate were measured with steady‐state fluorescence. Measurements were performed in dilute solutions of several fluid solvents at 25 °C and in a solid matrix of poly(methyl methacrylate) at room temperature. The values of I_E/I_M depended on the nature of the solvent, the emission wavelength, and the copolymer composition. Molecular dynamics simulations were performed for diastereoisomers of 2,4‐di(N‐carbazolyl)pentane and for isotactic and syndiotactic trichromophoric copolymer fragments to assist in the identification of the thermally accessible conformations capable of forming intramolecular excimers and the configurational relationship of the carbazole units in these complexes. Nearest neighbor carbazole groups made the dominant contribution to the excimers. Excimers were more likely in isotactic sequences than in syndiotactic sequences, as was also the case for the low‐energy excimer arising from the complete overlap of two carbazole units. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1272–1281, 2001