Effect of fullerene intercalation on the conformation and packing of poly-(2-methoxy-5-(3'-7'-dimethyloctyloxy)-1,4-phenylenevinylene)

Photoluminescence (PL) and resonance Raman spectroscopy are used to track changes in the conformations and packing of poly-(2-methoxy-5-(3'-7'-dimethyloctyloxy)-1,4-phenylenevinylene) (MDMO-PPV) chains with the addition of [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) molecules. PL lineshapes of MDMO-PPV thin films as a function of annealing time were first measured to determine the spectroscopic signatures of chain conformations and packing in the absence of PCBM. Annealing results in enhanced interchain interactions leading to red-shifts of PL 0-0 transitions by up to ～300 cm(-1) and apparent increases of the line shape Huang-Rhys factors. Wavelength-dependent PL lifetimes of as-cast and films annealed for short times (～30 s) are nonexponential with an instrument-limited component of ～100 ps and a ～350 ps component. With longer annealing times, decays become single exponential with an average lifetime of ～1 ns indicating that all excitations efficiently funnel to strongly coupled interchain sites. Addition of PCBM disrupts MDMO-PPV interchain interactions causing PL 0-0 transitions to blue-shift, increases in line width, and decreases in apparent Huang-Rhys factors. Resonance Raman spectra of MDMO-PPV/PCBM thin films with variable PCBM weight fractions (～50:1 up to 1:8 w/w) were then measured using short (488 nm) and long (568 nm) excitation wavelengths. The out-of-plane vinylene C-H wag mode of MDMO-PPV (～964 cm(-1)) showed pronounced increases in intensity of up to ～30% and red-shifts of up to 5 cm(-1) with increasing PCBM content. These changes result from a decrease of planarity between chain segments that suppresses interchain interactions. Furthermore, red-shifts of up to ～4 cm(-1) were observed for the C═C symmetric stretch of the MDMO-PPV vinylene group (～1625 cm(-1)) with 488 nm excitation. The sensitivity of the MDMO-PPV vinylene group vibrations with PCBM indicates preferential interactions between these two molecules and is consistent with intercalation of PCBM into the polymer structure. This assignment was confirmed by thermally annealing of MDMO-PPV/PCBM films to remove intercalated PCBM molecules, which partially restores interchain interactions as seen from smaller intensity increases (～15%) and red-shifts (～2 cm(-1)) of the ～964 cm(-1) mode. Overall, the spectroscopic results show that MDMO-PPV chains adopt distorted conformations (i.e., less intrachain order and shorter conjugation lengths) that have important implications for explaining the structural origins for large improvements in charge mobilities in MDMO-PPV/PCBM blends.     

Temperature effects on photoluminescence of poly [2-methoxy-5-(20-ethyl-hexyloxy)-1,4-phenylene vinylene]

We present photoluminescence studies as a function of temperature from poly [2-methoxy-5-(20-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV). The photoluminescence transition energies are red-shifted with decreasing temperatures that can be explained by the suppression of the torsional motion in the polymer backbone, which increased the effective conjugation length of the polymer. The enhancement of the relative intensity of the 0–1 to 0–0 vibronic band can be attributed to the formation of aggregates in coincidence with the vibronic 0–1 bands.     

Photo- and electro-luminescent properties of 5,10,15,20-tetra-p-tolyl-21H,23H-porphine doped poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] films

In this work we studied both photoluminescence (PL) and electroluminescence (EL) properties of 5, 10, 15, 20-tetra-p-tolyl-21H, 23H-porphine (TTP) doped poly[2-methoxy-5-(2′-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) with the weight percentages of 0, 0.5, 1, 3, 5, 8 and 12, respectively. In the process of PL the significant energy transfer occurs from MEH-PPV to TTP, even though there is a small spectral overlap between the absorption of TTP and the emission of MEH-PPV. For investigation of the process of EL a series of organic light-emitting diodes were fabricated with the device structure of ITO/PEDOT:PSS/TTP-doped polymer layer/Al (ITO = Indium Tin Oxides; PEDOT:PSS = poly (3,4-oxyethyleneoxythiophene): poly-(styrene sulfonate)). In devices in which the TTP was present at 5% the emission of EL was dominated by TTP; at lower doping levels MEH-PPV emission dominated. Moreover, multi-color emission was observed at the doping level below 5%. On the other hand, the mechanism for the EL process was reported.     

Energy distribution of trapping and transport states in MDMO-PPV ([poly-(2-methoxyl, 5-(3,77dimethyloctyloxy)] para phenylenevinylene)

We have investigated charge carrier transport and trapping in the layers of [poly-(2-methoxyl, 5-(3,77dimethyloctyloxy)] para phenylenevinylene (MDMO-PPV). To reveal distribution of the trapping states the thermally stimulated current method was applied using the varying excitation conditions by light and applied voltage. To assure the selective excitation of the defect states close to the band gap edges, both extrinsic and intrinsic excitation by the light passed through the long-pass color filters with the cut-off energies ranging from 1.77 eV up to 3.1 eV was employed. Carrier transport conditions were varied by increasing applied electric field from 5 x 10(4) V/cm up to 6 x 10(5) V/cm. The effective thermal activation energy of material conductivity was dependent both on the spectral region of the exciting light and applied electric field. The superposition of several thermally activated processes, i.e., carrier generation from the trapping states and thermally stimulated mobility growth according to the Gaussian disorder model, was revealed. The energy distribution of the trapping state density was shown to follow the Gaussian distribution function. We had demonstrated that carrier trapping is effectively influenced by the extended defect states with the effective activation energy values ranging from 0.05 eV up to 0.15 eV with maximum located at about 0.07-0.08 eV. Moreover, deeper states with activation energies of 0.28-0.3 eV and 0.8-0.85 eV were identified. The results are direct indication by photo-thermo-electrical methods of distributed in energy trapping and transport states with the standard deviation of the density of states of about 0.015 eV.     

Memory effect in a junction-like CdS nanocomposite/conducting polymer poly[2-methoxy-5-(2-ethylhexyloxy)1,4-phenylene-vinylene] heterostructure

The operation of a nonvolatile memory device is demonstrated using junction-like CdS nanocomposites embedded in a polymer matrix. The capacitance-voltage characteristics of Al/conducting polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene]/CdS nanocomposites in a polyvinyl alcohol matrix/indium tin oxide device exhibit hysteresis, which is attributed to the trapping, storage, and emission of holes in the quantized valence band energy levels of isolated CdS nanoneedles. The characteristics at different operating frequencies show that the hysteresis is due to trapping of charge carriers in CdS nanocomposites rather than in the interfacial states. The memory behavior in the inorganic/organic heterostructure is explained on the basis of a simple energy band diagram.     

Influence of the processing conditions on charge transfer and transport properties in poly(2-methoxy-5-(2′-ethylhexyloxy)1-4-phenylenevinylene):C60 composites for photovoltaics

Polymer-based photovoltaic devices have been elaborated by blending the conjugated polymer, poly(2-methoxy-5-(2′-ethylhexyloxy)1-4-phenylenevinylene) (MEH-PPV) with the buckminsterfullerene, C₆₀. The solvent used has a main influence on the optical and electrical properties of the photoactive layers. This could be attributed to different dispersion abilities of C₆₀ in the polymer layers shown by Atomic Force Microscopy and Scanning Electron Microscopy. Its effect on the transfer and transport properties has been studied. Thin film processing conditions have been modified by the preparation of blends of solutions of the polymer in Tetrahydrofuran and fullerene in Ortho-dichlorobenzene. The resulting spin casted layers show improved morphologies implying better dispersion of the fullerenes and increased short circuit currents. A decrease in the fullerene critical concentration to form percolation paths has been demonstrated. The improvement of the photovoltaic properties of the MEH-PPV/C₆₀ composites has been attributed to the nanosized fullerene domains formed upon phase separation. We used optical spectroscopy to study the charge transfer efficiency and electrical measurements to investigate charge transport properties in MEH-PPV:C₆₀.     

Electroluminescence of zinc selenium (ZnSe) nanocrystals co-doped with poly[2-methoxy-5-(2'-ethylhexyloxy-p-phenylenevinylene)] (MEH-PPV)

We have synthesized water soluble zinc selenium (ZnSe) nanocrystals by using mercaotoacetic acid (TGA) as the stabilizer. The synthesized ZnSe nanocrystals were co-doped with poly[2-methoxy-5-(2'-ethylhexyloxy-p-phenylenevinylene)] (MEH-PPV) to fabricate an organic/ inorganic hybrid multilayer light-emitting device (LED). The structure of the device was indium-tin-oxide (ITO)/poly (ethylene-dioxythiophene):poly(styrenesul-fonate) (PEDOT:PSS)/MEH-PPV:ZnSe/bathocuproine (BCP)/tris-(8-hydroxylquinoline)-aluminum (Alq3)/Al. We demonstrate that the device has a lower driving voltage and increased current densities and power efficiencies owing to the co-doped ZnSe quantum dots. We obtained good efficiency of the devices when the quality ratio of MEH-PPV and ZnSe quantum dots was 1:1.     

Carrier transport and luminescence properties of nanocomposites of poly[2-methoxy-5-(2-ethyl hexyloxy)-p-phenylene vinylene] and dehydrated nanotubes titanic acid

The carrier transport capability and luminescence efficiency of poly(2-methoxy-5-(2-ethyl hexyloxy)-p-phenylene vinylene) (MEH-PPV) films are enhanced by doping with dehydrated nanotubed titanic acid (DNTA). MEH-PPV molecules, either wrapped on the outer surface of or encapsulated into DNTA pores, have a more open, straighter conformation than undoped molecules, which induces a longer conjugated backbone and stronger interchain interactions, thereby, enhancing carrier mobility. MEH-PPV molecules within DNTA pores have higher exciton recombination efficiency owing to quantum confinement and the antenna effect.     

聚(2,5-二羟基-1,4-苯撑吡啶并二咪唑)纤维的性能与应用

介绍了[聚(2,5-二羟基-1,4-苯撑吡啶并二咪唑)](PIPD)纤维的制备、性能及应用,PIPD纤维的强度和模量高,具有耐热、阻燃和耐化学稳定性等优良性能,尤其具有良好的压缩和扭曲性能,高电阻特性以及与树脂基体优良的粘结性能,PIPD纤维可作为耐热材料、增强材料、防弹冲击材料、电绝缘材料而广泛应用于航空军事等领域.     

Resonant infrared matrix-assisted pulsed laser evaporation of CdSe colloidal quantum dot/poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-(1-cyano vinylene)phenylene] hybrid nanocomposite thin films

CdSe colloidal quantum dot / poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-(1-cyano vinylene)phenylene] hybrid nanocomposite thin films were deposited using resonant infrared matrix-assisted pulsed laser evaporation. The distributions of CdSe colloidal quantum dots within the polymer matrices of as-grown films were evaluated using transmission electron microscopy, and the optical properties of these films were determined by photoluminescence spectroscopy. These measurements demonstrate that: i) depending upon the deposition parameters used, the CdSe colloidal quantum dot distribution can be tuned between two morphology extremes, i.e. clustering or homogenous dispersion; and ii) the constituent materials of the nanocomposite are not damaged in any way that affects structural or optical properties by the deposition process. The demonstrated ability to control nanoparticle distribution within organic films has not been achieved by other deposition techniques and could enhance the performance of optoelectronic devices based on these materials.     

Photocurrent generation in a CdS nanocrystals/poly[2-methoxy-5-(2′-ethyl-exyloxy)phenylene vinylene] electrochemical cell

In this paper the photoelectrochemical processes occurring in composites formed of organic-capped CdS nanocrystals and low molecular weight poly[2-methoxy-5-(2′-ethyl-exyloxy)phenylene vinylene] conjugated polymer were investigated. High quality colloidal CdS nanoparticles were synthesized by means of thermal decomposition of suitable precursors in non coordinating solvents, using oleic acid as surface capping agent.

The absorption and emission properties of the prepared heterojunctions were studied both in solutions and in composite films.

The dispersed hybrids were also investigated as photoactive materials, focusing on the photoinduced charge transfer and recombination processes at the interface between the two components. The composites have shown a fundamental role in photoelectrochemical applications due to the presence of a great number of interfaces able to enhance the charge transfer between mixture components.

Blend solutions prepared with octylamine capped CdS nanocrystals showed an improvement of the photoconductivity with respect to hybrids containing longer oleate surfactants.     

Cell viability measurement using 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein acetoxymethyl ester and a cantilever sensor

Detection of viable pathogenic bacteria has widespread application in food safety and human health. Antibody-based methods require a growth step which limits time-to-results performance. In this study, we use a mass-change sensitive cantilever biosensor and a probe, 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein acetoxymethyl ester (BCECF-AM), that accumulates only in live cells inducing a mass-change response to determine the cell viability in a short time. A poly-L-lysine coated sensor immobilized with live Escherichia coli JM101 (a surrogate for a pathogenic target) at various concentrations was exposed to BCECF-AM in a flow arrangement. A larger resonant frequency decrease in response to 100 μL of 60 μM BCECF-AM was observed when the sensor surface cell concentration was increased from 1?090 ± 580 to 3?960 ± 370 cells/mm(2) (n = 5). A log-linear relationship between the sensor surface cell concentration and frequency response was obtained in the range of 1?000-4?000 cells/mm(2) and as low as ～2?000 viable E. coli cells were rapidly detected (<1 h).     

溴甲基化法合成聚[2-甲氧基-5-(2’-乙基己氧基)对苯乙炔]

以对甲氧基苯酚和溴代异辛烷为原料,经醚化、溴甲基化、脱溴化氢反应,成功合成聚[2-甲氧基-5-(2’-乙基己氧基)对苯乙炔](MEH-PPV),其数均分子量为5.7×104。利用傅立叶变换红外光谱(FTIR)、核磁共振波谱(1H-NMR)及紫外可见分光光谱(UV-Vis)对中间产物及MEH-PPV进行结构表征,结果表明,合成的中间产物和MEH-PPV分子结构与文献报道的一致。     

离子注入改性聚[2-甲氧基-5-(3''''-甲基)丁氧基]对苯乙炔微观结构与性能

采用低能氮正离子(N )对π共轭高分子聚[2-甲氧基-5-(3'-甲基)丁氧基]对苯乙炔(MMB-PPV)薄膜进行离子注入改性,注入剂量为9.6×1016 ions/cm2,能量为30 keV.利用红外光谱、紫外-可见吸收光谱、X射线衍射、透射电镜及热失重等手段对离子注入改性MMB-PPV薄膜的微观结构及热学性能进行研究.红外光谱显示,注入后分子侧链烷氧取代基的C-H振动峰强度减弱,同时在3442、1622 cm-1等处出现了N-H键的振动峰;薄膜的紫外-可见吸收光谱向长波方向移动,且在可见光区范围内的吸收强度增加;离子注入使聚合物分子链排列更加规整,取向度明显增大,结晶性能大大改善;经过离子注入后,聚合物材料的初始分解温度由未注入时的245.64 ℃提高至280.52 ℃,分子的热稳定性能显著增强.     

Study of the zero-field magnetic ordering, charge fluctuation and trapping in the oxo-bridged heterometallic acetylacetonate complex Fe3YO6R3[Y11(C5O2H7)33]; (R = C5H7)

The Mössbauer, magnetic susceptibility and EXAFS data for the oxo-bridged heterometallic acetylacetonate Fe₃YO₆R₃[Y₁₁(C₅O₂H₇)₃₃] (R = C₅H₇) are analyzed in terms of a bound-to-free model describing the transition from the state of delocalized valence, denoted Fe_deloc ^(3–)+, in the magnetically disordered paramagnetic complex at 300 K to the states of localized valence, denoted Fe_loc ²⁺ and Fe_loc ³⁺, in the magnetically ordered complex at 4.2 and 77 K.     

Charge photogeneration and recombination in poly[2-methoxy-5-(2′-ethyl-hexoxy-p-phenylene vinylene]:fullerene composite films studied by photocurrent response

The photocurrent spectral responses of poly[2-methoxy-5-(2′-ethyl-hexoxy-p-phenylene vinylene]:fullerene (C60) composites are measured as a function of C60 concentration. At low concentration, the relationship between the external quantum efficiency (EQE) and absorption spectra is exhibited as the strengthened antibatic effect, and the EQE of the composite devices declines with increasing concentration of C60. At higher concentration, however, the maximum EQE gradually coincides with the absorption peak (symbatic response) and the EQE of composite devices begins to increase with increasing C60 concentration. It is proposed that at low concentration, dopant C60 increases the self-absorption rate of composite films, and charge trapping by C60 molecules causes the loss of efficiency. At high C60 concentration, the large-scale aggregations in composite films build pathways for charge carrier transport to respective electrodes, inhibiting the self-absorption effect and charge recombination on C60.     

Electrophoretic deposition of poly[3-(3-N,N-diethylaminopropoxy)thiophene] and composite films

Poly[3-(3-N,N-diethylaminopropoxy)thiophene] (PDAOT) was prepared by oxidative polymerization and investigated by ultraviolet (UV), Raman and nuclear magnetic resonance (NMR) spectroscopies. Protonated PDAOT was dissolved in water or ethanol/water mixtures and deposited by cathodic electrophoretic deposition (EPD) on conductive substrates. Film thickness was varied in the range of 0–5 μm by controlling the deposition voltage and deposition time. PDAOT was found to form strong supramolecular interactions with single-walled carbon nanotubes (SWNTs), allowing the formation of stable and concentrated nanotube dispersions, which were used for the formation of composite PDAOT–SWNT films by EPD. Furthermore, introduction of ZnO particles to the PDAOT solutions also allowed the formation of PDAOT–ZnO composite films by EPD. The composition of the films was varied by changing the concentration of SWNTs and ZnO in the suspensions. The dispersion of ZnO particles was improved using protonated dopamine (DA) as a dispersant. The deposits were studied by X-ray analysis (XRD), thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray diffraction and scanning electron microscopy (SEM).     

Preparation, characterization, and optical properties of disulfide-comprising oligo[2,5-bis(thiomethyl)-1,4-dithiane] and its poly[S-alkylcarbamate]

Novel poly[S-alkylcarbamate]s were prepared by polyaddition of oligo [2,5-bis(thiomethyl)-1,4-dithiane] (oligo[BMMD]) with isocyanate for optical polymers having high refractive indices (nD) and Abbe's numbers (D). Oxidation of 2,5-bis(mercaptomethyl)-1,4-dithiane (BMMD) with ferric chloride or methylsulfoxide gave oligo[BMMD] in a mixture of n-mers (typically n = 1–6) by disulfide-forming propagation. The use of the former oxidant giving mainly BMMD dimer appeared to be preferable for the subsequent preparation of transparent poly[S-alkylcarbamate]. With 1,3-bis(isocyanatomethyl)cyclohexane, 1,6-diisocyanatohexane, or 1,3,5-tris(isocyanatomethyl)cyclohexane, nD:D values of poly[S-alkylcarbamate]s ranging from 1.609:38.0 to 1.659:35.6 were comparable to those of flint glasses. Copoly[S-alkylcarbamate]s were prepared using 2-mercaptoethylsulfide or 2-mercaptoethylether for modification of nD and D. Contribution of the disulfide bond and the 1,4-dithiane ring in oligo[BMMD] to increase nD is discussed in terms of molar refraction. Suppressed UV absorption of the polymer, which caused high D, was attributed to the trans-gauche-trans conformation around the disulfide bond. This work shows that oligo[BMMD] serves as a useful material for the preparation of polymers having high nD and high D and that poly[S-alkylcarbamate]s thus obtained are promising optical materials.