Synthesis, characterization, and nonlinear optical properties of donor–acceptor conjugated polymers and polymer/Ag nanocomposites

Two new donor–acceptor (D–A) conjugated polymers P1 and P2 containing 3,4-didodecyloxythiophene and 1,3,4-oxadiazole units are synthesized via Wittig reaction methodology. Cyclic voltammetry studies reveal that the polymers are both p and n dopable, and possess low-lying LUMO energy levels (?3.34?eV for P1 and ?3.46?eV for P2) and high-lying HOMO energy levels (?5.34?eV for P1 and ?5.27?eV for P2). The optical band gap of the polymers is in the range of 2.25–2.29?eV, calculated from the onset absorption edge. The polymers emit orange to yellow light in the film state when irradiated with a UV light. The synthesized polymers are used to prepare polymer nanocomposites with different wt% of silver nanoparticles. The polymer nanocomposites are characterized by UV–Vis absorption spectroscopy, field emission scanning electron microscopy, and thermogravimetric analysis. Both polymers and polymer/Ag nanocomposites show good thermal stability with onset decomposition temperature around 300?°C under nitrogen atmosphere. The nonlinear optical properties of polymers and polymer/Ag nanocomposites are measured by Z-scan technique. Both polymers and polymer nanocomposites show a good optical limiting behavior. Nearly five times enhancement in the nonlinear optical properties is observed for polymer/Ag nanocomposites. The value of effective two-photon absorption coefficient (β) is in the order of 10^?10–10^?11?m/W. These results indicate that the synthesized polymers (P1 and P2) and their Ag nanocomposites are expected to be good candidates for application in photonic devices.     

Synthesis and photovoltaic properties of benzotriazole-based donor–acceptor copolymers

Two new D–A copolymers containing benzotriazole (BTz) acceptor unit and different donor units of benzodithiophene (BDT) and 2,7-carbazole, PBDT-DTBTz and PC-DTBTz, were synthesized for the application as donor materials in polymer solar cells (PSCs). By changing the donor units, the band gaps and the highest occupied molecular orbital (HOMO) energy levels of the copolymers could be finely tuned. PC-DTBTz exhibited the lower HOMO energy level of ?5.34 eV, and the lower HOMO energy level can lead to a higher open-circuit voltage (V _oc) of 0.73 V in PC-DTBTz-based devices. The PCEs of the PSCs based on PBDT-DTBTz and PC-DTBTz blends with [6,6]-phenyl-C₆₁ butyric acid methyl ester (PC₆₁BM) were 1.55 and 1.33 %, respectively, under the illumination of AM1.5, 100 mW/cm².     

Synthesis,characterization, and photovoltaic properties of acceptor–donor–acceptor organic small molecules with different terminal electron-withdrawing groups

Two soluble acceptor–donor–acceptor (A–D–A) type organic small molecules, 2,2′-(5,5′-(1E,1′E)-2,2′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(ethene-2,1-diyl)bis(3,4-dihexylthiophene-5,2-diyl))bis(methan-1-yl-1-ylidene)dimalononitrile (BvT-DCN) and 2,2′-(3,3′-(1E,1′E)-2,2′-(5,5′-(1E,1′E)-2,2′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(ethene-2,1-diyl)bis(3,4-dihexylthiophene-5,2-diyl))bis(ethene-2,1-diyl)bis(5,5-dimethylcyclohex-2-ene-3-yl-1-ylidene))dimalononitrile (BT-C6), were synthesized by Knoevenagel condensation reaction based on benzothiadiazole, thiophene, and different terminal electron-withdrawing groups. The acceptor group benzothiadiazole and donor group thiophene inside the molecules are connected by all-trans double bonds, which ensures the benzothiadiazole and thiopene groups are in the same plane and makes the molecules have a relative narrow band gap and absorb sunlight in the long wavelength. The terminal electron-withdrawing groups, malononitrile and 2-(5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (DCM), are symmetrically introduced into the molecules, respectively, to tune the energy level and extend the absorption of the molecules. The UV–Vis absorption spectrum and cyclic voltammetry measurements indicated that BT-C6 has a lower energy band gap (1.60 eV) than BvT-DCN (1.71 eV), which arises from the stronger electron-withdrawing ability of DCM group in BT-C6 than that of malononitrile group in BvT-DCN. And BvT-DCN and BT-C6 have nearly the same highest occupied molecular orbital energy level, ?5.74 eV for BvT-DCN and ?5.72 eV for BT-C6 due to the same electron–donor group of the two compounds. Bulk heterojunction photovoltaic devices were fabricated using BvT-DCN or BT-C6 as donor and (6,6)-phenyl C₆₁-butyric acid methyl ester as acceptor. The device based on BT-C6 has a higher (~8 times) short circuit current and power conversion efficiency than the device based on BvT-DCN, resulting from the wider solar light absorption of BT-C6 and smaller phase separation dimension of the active layer based on BT-C6.     

Synthesis and characterization of Y-shape electron donor–acceptor type organic dyes for dye-sensitized solar cells

Three Y-shape organic dyes, (Z)-3-(5-(3,5-bis(4-(9H-carbazol-9-yl)styryl)-4-methoxyphenyl)thiophen-2-yl)-2-cyanoacrylic acid (OD-1), (Z)-3-(5′-(3,5-bis(4-(9H-carbazol-9-yl)styryl)-4-methoxyphenyl)-2,2′-bithiophen-5-yl)-2-cyanoacrylic acid (OD-2) and (Z)-3-(5′-(3,5-bis(4-(9H-carbazol-9-yl)styryl)-4-methoxyphenyl)-3,4′-4″-trithiophenyl-5-yl)-2-cyanoacrylic acid (OD-3) were synthesized and used as sensitizers in nanocrystalline dye-sensitized solar cells (DSSCs). The introduction of the bis(carbazolylstyryl) units as an electron donor group and oligothiophene units as a both electron donors and π-spacers increased the conjugation length of the sensitizers and thus improved their molar absorption coefficient and light harvesting efficiency. DSSCs with the configuration of SnO₂:F/TiO₂/organic dye/liquid electrolyte/Pt devices were fabricated using these OD-1, OD-2 and OD-3 as a sensitizers. Among the devices, the DSSC composed of OD-3 exhibited highest power conversion efficiency of 3.03% under AM1.5G (100 mW cm⁻²).     

Synthesis and characterization of semiconductor polymers having different phenylene–vinylene conjugation lengths

We have synthesized phenylene–vinylene (PV) polymers containing segments with different conjugation lengths interspaced by random distributed aliphatic segments. Infrared (IR) and ultraviolet–visible (UV–vis) spectroscopies, hydrogen nuclear magnetic resonance (¹H NMR) spectrometry and differential scanning calorimetry (DSC) were used to characterize the prepared copolymers’ structures. Polymers molecular weights were determined by gel permeation chromatography (GPC). The effect of polymer structure and composition on emission properties was studied by fluorescence (PL) spectroscopy under different irradiation wavelength. The emission energy shift due to segments with longer conjugation lengths was minor owed to the low polymerization degree achieved.     

Multifunctional donor–acceptor conjugated polymers containing isoindigo and benzothiadiazole moieties for electrochromic,photoelectric sensor, 2,4,6-trinitrophenol detection and resistance memory device

Journal of Materials Science - Six novel donor–acceptor conjugated polymers were designed and synthesized by the Stille coupling reaction of triarylamine derivatives as donor units with...     

Optical characterization of a new donor–acceptor type conjugated polymer derived from 3,4-diphenylthiophene

A new donor–acceptor type poly{2-(3,4-didecyloxythiophen-2-yl)-5-[3,4-diphenyl-5-(1,3,4-oxadiazol-2-yl)thiophen-2-yl]-1,3,4-oxadiazole} (P1) has been designed and synthesized starting from thiodiglycolic acid, 1,2-diphenylethane-1,2-dione, and diethyl oxalate through multi-step reactions using precursor polyhydrazide route. The charge-transporting and linear optical property of the polymer has been investigated by cyclic voltammetric, UV–visible, and fluorescence emission spectroscopic studies. The UV–visible absorption spectrum of polymer in thin film form showed maxima at 420 nm. The polymer displayed bluish-green fluorescence both in solution and thin film form. The optical band gap is determined to be 2.27 eV. Third-order nonlinear optical property of the new polymer has been investigated at 532 nm using single beam Z-scan and degenerate four wave mixing (DFWM) techniques with nanosecond laser pulses. The absorptive nonlinearity observed for the polymer P1 is of optical limiting type, which arises due to an “effective” three-photon absorption (3PA) process. The third-order nonlinear optical susceptibility (χ⁽³⁾) of the polymer is found to be 0.831 × 10^–12 esu. Both linear and nonlinear optical studies revealed that the new polymer (P1) is a promising material for applications in photonic devices.     

Synthesis and characterization of bismaleimide–polyetherimide–titania hybrid

Ternary hybrids of bismaleimide–polyetherimide–titania were synthesized by sol–gel reaction and characterized by Scanning Electron Microscope, Energy Dispersive X-ray Analysis, Thermogravimetric Analysis and Differential Scanning Calorimeter. Moreover, their mechanical properties were also measured.The results indicated that titania could be introduced into the blends of bismaleimide–polyetherimide(BMI/PEI) by sol–gel reaction. Although, the titania content in BMI-rich phase was higher than that in PEI-rich phase, the titania particles dispersed in the hybrids were almost uniform. The introduction of titania actually changed the ultimate phase structure of the PEI modified BMI system because of the chelate complex formation between o,o′-diallyl bisphenol A and dibutoxy bis(acetylacetonato) titanium (IV), which was proved by their ultraviolet spectra. If the content of titania was increased under a specific PEI content, the morphology of the bismaleimide–polyetherimide–titania hybrids remained unaffected apparently, while its mechanical properties were obviously improved.     

Synthesis and characterization of a new liquid polymer precursor for Si–B–C–N ceramics

A new liquid polyborosilazane precursor for Si–B–C–N ceramic was synthesized by co-condensation reaction of boron trichloride, organodichlorosilanes, and hexamethyldisilazane. The structure and properties of polyborosilazane were studied by means of Fourier transform-infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), rheology, and thermogravimetric analysis (TGA). The conversion of polymer to ceramic and the high-temperature behavior of the new polymer-derived ceramic were investigated by TG–MS, FT-IR, X-ray diffraction (XRD) and high-temperature TGA (HTGA). The ceramics showed good oxidative resistance and thermal stability with weight gain of 1.8 wt% at 1350 °C under air atmosphere and weight loss of 2.6% at 1900 °C under Ar atmosphere.     

Novel styrene polymers functionalized with phosphorus–nitrogen containing molecules: Synthesis and properties

A phosphorus and nitrogen-containing compound with high phosphorus content, AC₂NP₂, was firstly synthesized by the Kabachnik–Fields reaction and followed by esterification with acryloyl chloride. The synthesized comonomer was then incorporated into different amounts of polystyrene via radical solution polymerization. The copolymers were well characterized using Fourier transform infrared (FTIR), UV/vis spectrophotometer, nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), microscale combustion calorimeter (MCC) and LOI. The results showed that the AC₂NP₂ was easily incorporated into the backbone of polystyrene, and the copolymers prepared have high transparency. The glass transition temperature (T_g) of the copolymers was decreased with increasing the AC₂NP₂ content, due to the introduction of much more flexible molecular chain. The TGA results revealed that the introduction of AC₂NP₂ units slightly decreased the initial decomposition temperatures, but significantly improved the thermal stability of copolymers at high temperature regions under both nitrogen and air atmosphere. Furthermore, all the copolymers exhibited much lower flammability as compared with virgin polystyrene.     

Synthesis and characterization of hollow glass–ceramics microspheres

Hollow glass–ceramics microspheres (HGCMs), with the diameter from 10 to 60 μm and the shell thickness less than 2 μm, were successfully fabricated by a simple technique using polyacrylamide microspheres (PAMs) as template. The corresponding HGCM were obtained after a thermal treatment of the core–shell microspheres, which were synthesized with organic template method. The size, morphology and phase composition of synthesized products were determined via XRD, SEM, TGA. The effects of the amount of glass powder, the Hydrophile–Lipophile Balance (HLB) value, the sintering temperature, and the ratio of pre-adsorbed water to the water in the slurry on the morphologies of HGCM have been investigated. The results showed that the agglomeration of HGCM can be reduced by adjusting the HLB value. In addition, the amount of solid beads decreases obviously by reducing ratios and adjusting the HLB value. As the sintering temperature increases, the surface of the HGCM becomes smooth and compact. Meanwhile, computational investigations are carried out to better understand the strengthen effect of taking glass–ceramics materials in the system MgO–Al₂O₃–SiO₂ (MAS) as shell materials.     

Synthesis and characterization of chitosan–carbon nanotube composites

Acid functionalized single walled carbon nanotubes were covalently grafted to chitosan by first reacting the oxidized carbon nanotubes with thionyl chloride to form acyl-chlorinated carbon nanotubes which are subsequently dispersed in chitosan and covalently grated to form composite material, CNT–chitosan, 1, which was washed several times to remove un-reacted materials. This composite has been characterized by FTIR, 13C NMR, TGA, SEM and TEM and has been shown to exhibit enhanced thermal stability. The reaction of 1, with poly lactic acid has also been accomplished to yield CNTchitosan–g-poly(LA), 2 and fully characterized by the above techniques. Results showed covalent attachment of chitosan and chitosan–poly lactic acid to the carbon nanotubes.     

Synthesis and characterization of gold–polypyrrole film composite

Polypyrrole (PPy) coatings have potential applications in batteries, fuel cells, sensors, anti-corrosion coatings, and drug delivery systems. In this article, PPy film coating on the electrode of quartz crystal microbalance (QCM) was exposed to acidic aqueous HAuCl₄ solution. The reduction for gold ions took place and gold particles were produced at the film surface. The gold content at the PPy film was monitored by using QCM. The concentration of gold uptake increases as the original concentration of HAuCl₄ solution increases. The morphology of the film before and after the deposition of the gold particles was studied by the scanning electron microscopy coupled with energy dispersive X-ray spectrometry. The gold particles are of undefined shape and have diameters around 200–600 nm. However, the image of the composite powder shows that gold particles of sizes 100–120 nm are distributed over the surface of the polymer particles with some aggregation. Infrared spectroscopy and X-ray diffraction were used to characterize the composite.     

Synthesis and characterization of barium ferrite–silica nanocomposites

In this work, we prepared barium ferrite-silica (BaM-SiO₂) nanocomposites of different molar ratios by high-energy ball milling, followed by heat-treatment at different temperatures. The microstructure, morphology and magnetic properties were characterized for different synthesis conditions by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). The results indicate that 15 h of milling was enough to avoid the generation of hematite phase and to get a good dispersion of barium ferrite particles in the ceramic matrix. For milling periods beyond 15 h and heat treatment above 900 °C, the XRD patterns showed the presence of hematite phase caused by the decomposition of BaM. The agglomerate size observed through SEM analysis was around 150 nm with a good BaM dispersion into the SiO₂ matrix. The highest saturation magnetization (Ms) value obtained was 43 emu/g and the corresponding coercivity (Hc) value of 3.4 kOe for the composition 60BaM-40SiO₂ milled for 15 h and heat treated at 900 °C. This coercivity value is acceptable for the application in magnetic recording media.     

Synthesis and characterization of photoconductive C60–N-vinylcarbazole copolymers

Soluble C60–N-vinylcarbazole copolymers with different C60 contents were synthesized in lithium naphthalene-initiated anionic polymerization reactions. 13C nuclear magnetic resonance (NMR) results provided strong evidence for the covalent attachment of poly(N-vinylcarbazole; PVK) units to the C60 cores. The chemical shifts located at 142.16, 143.21, 144.70, 145.61, 146.65, 147.09, 149.08 and 170.28 p.p.m. in the 13C NMR spectrum of the copolymer are assigned to the unsaturated carbon signals of the substituted C60 cage. Its ultraviolet–visible absorption spectrum tends to move to the longer wavelength compared with those of the N-vinylcarbazole (NVC) monomer and PVK, and the peak range also extended from about 350 to 640 nm due to charge-transfer interaction between C60 and N-ethylcarbazole units. X-ray diffraction evidence suggests that the structure of the resultant copolymer might be a layered structure. Like the C60 chemically modified PVK, this material also exhibits good photoconductivity and temperature sensitivity. An unusual temperature dependence of the ESR spectrum is observed. In addition, it is also found that both [60] fullerene polyanion salts [(Cn-60) M+n, M=Li, Na, K] and fullerene itself are unable to initiate the polymerization of such monomers as N-vinylcarbazole, styrene and acrylonitrile, etc. © 1998 Kluwer Academic Publishers     

Miscibility and morphology of poly p-phenylene sulphide–liquid crystal polymer blends

Blends of poly p-phenylene sulphide (PPS) and a liquid crystalline polymer (LCP) were made by two methods: (i) mixing and capillary extrusion (samples A), and (ii) injection moulding (samples B). To study miscibility in the melt and solid states and the resulting morphology, techniques like polarized light optical microscopy, capillary rheometry, dynamic mechanical thermal analysis and scanning electron microscopy with X-ray microanalysis were used. It was observed that the miscibility of the amorphous fractions of both polymers increased with increasing intensity (rates and stresses) of deformational flow (shear and elongational). Samples A had a morphology composed of fibrils of both polymers, but a matrix made of only one polymer i.e. PPS. Samples B had a mainly fibrillar morphology, with no observable matrix, made of both polymers. Formation of pure LCP fibrils was not observed neither in the extruded blends nor in the injection moulded samples. The addition of LCP to PPS improved its mechanical properties. At a molecular level, these blends can be considered to be molecular composites.     

Pulsed laser deposition film of a donor–acceptor–donor polymer as possible active layer in devices

A molecule having a ketone group between two thiophene groups was synthesized. Presence of alternating electron donating and accepting moieties gives this material a donor–acceptor–donor (DAD) architecture. PolyDAD was synthesized from DAD monomer by oxidative polymerization. Device quality films of polyDAD were fabricated using pulsed laser deposition technique. X-ray photoelectron spectroscopy (XPS) and fourier transform infrared spectra (FTIR) data of both as synthesized and film indicate the material does not degrade during ablation. Optical band gap was determined to be about 1.45 eV. Four orders of magnitude increase in conductivity was observed from as synthesized to pulsed laser deposition (PLD) fabricated film of polyDAD. Annealing of polyDAD films increase conductivity, indicating better ordering of the molecules upon heating. Rectifying devices were fabricated from polyDAD, and preliminary results are discussed.