Donor–acceptor copolymers based on benzo[1,2-b:4,5-b′]dithiophene and pyrene-fused phenazine for high-performance polymer solar cells

Two novel donor–acceptor (D–A)-type conjugated polymers of PTTPPz-BDT and PTTPPz-BDTT were successfully synthesized by Stille coupling polymerization, in which 7,8-dialkoxy benzo[1,2-b:4,5-b′]dithiophene (BDT) and 7,8-bithienyl benzo[1,2-b:4,5-b′]dithiophene (BDTT) were used as donor units, thiophene and pyrene-fused phenazine (PPz) were employed as π-bridges and acceptor units, respectively. High carrier mobilities, broad absorption spectra, narrow optical band gaps, and low HOMO energy levels were observed for both polymers. Furthermore, high-efficiency photovoltaic performance with power conversion efficiency (PCE) over 4.25% was exhibited in their polymer solar cells (PSCs) using [6,6]-phenyl-C₇₁-butyric-acid-methyl-ester (PC₇₁BM) as acceptor. The maximum PCE of 4.86% with short-circuit current density of 11.10 mA cm⁻² and fill factor of 62.5% was obtained in the PTTPPz-BDTT based cell. These results indicate that incorporating large planar PPz moiety into D–A-type copolymer is an efficient approach to improve photovoltaic performance for PSCs.     

Evidence from surface tension and fluorescence data of a pyrene-assisted micelle-like assemblage of humic substances

Surface activity and fluorescence of humic substances (HS) and HS/pyrene solutions were monitored under various pH conditions. For HS alone the surface tension of the solutions decreased with increasing acidity, with a minimum at around pH 4. This effect, which is a consequence of an increase in the amphiphilic character of structures, is much more pronounced in humic (HA) than in fulvic acids (FA). The addition of pyrene (0.1 micromolL(-1)) results, for HA, in a marked reduction in the migration of amphiphilic species to the solution surface. FA profiles are not modified in presence of pyrene at that concentration. A decrease in the pyrene I1/I3 ratio in HS solutions shows that below pH 9 pyrene molecules react progressively to the change to a more hydrophobic environment, the greatest effect being observed at around pH 6 to 7. These signals are followed by a significant increase in the pyrene excimer fluorescence (lambda(exc)/lambda(em)=334 nm/450 nm), which is a consequence of the proximity of pyrene molecules. For FA, the I1/I3 decrease is less significant and no excimers develop. This set of effects is explained in view of conformational adjustments of HS, mainly HA, which become arranged in micelle-like domains in aqueous solution, the aromatic moieties being assembled around the pyrene molecules.     

Quantitative analysis of the cross-linked structure of microgels using fluorescent probes

Properties of polymeric microgels are influenced by the internal polymer cross-linked structure, but tools to quantitatively analyze this internal structure are limited. With the finding that polymer networks alter the diffusivity and subsequent excimer formation of pyrene, this study used the ratio between pyrene excimer and monomer emission to determine the number of cross-links (N) and average pore size (ξ) in poly(ethylene glycol) diacrylate (PEGDA) microgels. A calibration curve to relate pyrene emission to N and ξ in PEGDA hydrogels was prepared and used to calculate N and ξ in PEGDA microgels. The pyrene emission indicated that PEGDA microgels had a higher cross-linking density and a smaller average pore size when compared with bulk cross-linked hydrogels of the same PEGDA concentration. The analytical method demonstrated in this study may be useful for fine-tuning polymeric microgel properties for a broad array of applications.     

Electrochemical fabrication of neuron-type networks based on crystalline oligopyrene nanosheets

Electrochemical polymerization of pyrene in boron trifluoride diethyl etherate (BFEE) produced oligopyrenes (pyrene oligomers) with repeat unit numbers of 2-15. The oligoyrenes grown at the working electrode are nanosheets with high crystallinity. As an array of microelectrodes or a semiconductive silicon wafer patterned with microelectrodes were used as the working electrode, a dendritic network of cyrstalline oligopyrene nanosheets was fabricated. The initially grown nanosheets on the microelectrodes act as nodes and the network with interconnects of the nanosheets grow from the nodes. The number and structure of the inconnectects can be controlled by the structure of the patterned electrode, the concentration of the monomer, the value of applied potential and the charge density used for electrochemical deposition. This is the first example of fabrication neuron-type network based on conductive organic nanosheets.     

Novel 4-(2,2-diphenyl-vinyl)-phenyl substituted pyrene derivatives as efficient emitters for organic light-emitting diodes

Two pyrene derivatives (PVPP and TPVPP) bearing 4-(2,2-diphenyl-vinyl)-phenyl side unit were developed for organic light-emitting diodes. Their photophysical, thermal, electrochemical, and electroluminescent properties as well as the film morphologies have been investigated in detail. Both of them exhibit high solid-state quantum yields, good thermal stability, and high glass-transition temperatures in the range of 127–150 °C. In particular, it is found that multiple side units can significantly affect the electrochemical properties to improve the electron injection. The LUMO energy level of TPVPP is −2.76 eV, which is very close to that of commonly used electron transport materials. The maximum luminance of OLED devices using TPVPP as an emitter layer is 103835 cd/m² with a maximum current efficiency of 5.19 cd/A and a maximum power efficiency of 3.38 lm/W.     

Sorption-Desorption of Pyrene for Colombia and New Mexico Soils

The adsorption and availability of polycyclic aromatic hydrocarbons (PAHs) in the environment is an important factor to be considered for potential bioremediation processes. If desorption of the organic occurs, it could imply that remediation technologies such as microbial degradation may be feasible for PAH contaminated soils. Conversely no, or partial, desorption would indicate that the components may persist in the environment due to their decreased bioavailability. The sorption-desorption of pyrene in conjunction with two different soils was studied to determine the feasibility of bioremediation as an effective treatment. The measured distribution coefficient (K _d ) for the Colombia and New Mexico soils using a 4:40 soil:liquid ratio was 1956 and 526 L/kg, respectively. When the soil:liquid ratio was reduced to 1:40, the K _d values were 4294 L/Kg for the Colombia, and 1141 L/Kg for the New Mexico soil.     

Theoretical study of α-fluorenyl oligothiophenes as color tunable emissive materials for highly efficient electroluminescent device

The modifications of α-fluorenyl oligothiophenes by adding carbazole and pyrene end-capped moieties have been carried out using density functional theory (DFT) and time-dependent DFT (TD-DFT) method. The ground state conformation, energy gap, absorption, and emission properties as well as the change of λ_abs when oligothiophenes were increased up to 4 units have been investigated. We have fine-tuned the energy level and emission color by adjusting the conjugation length of the thiophene units connected to fluorene moieties. The results are pointed out that the excitation energies obtained by TD-DFT were decreased when the conjugation length was extended which strongly correspond to experimental observations, OLED devices of these materials emitted brightly in various colors from deep blue to orange with good color qualities and luminance efficiencies.     

阳离子型Gemini表面活性剂共振光散射法测定DNA及相互作用机理的研究

在酸性介质(pH=3.51)中,脱氧核糖核酸(DNA)能显著地增强阳离子型Gemini表面活性剂(G14-4-14)的共振光散射信号,据此提出了G14-4-14共振光散射法测定DNA的新方法,并对介质酸度、离子强度、G14-4-14浓度及共存物质干扰等实验条件进行了优化。在最佳条件下绘制了工作曲线,该方法线性范围为0～2760μg.L-1,检出限为7.79μg.L-1,用于合成样品的测定,结果令人满意。以芘(pyrene)为荧光探针,应用稳态荧光法探讨了G14-4-14与DNA的相互作用,并运用红外光谱及共振光散射光谱初步探讨了G14-4-14与DNA相互作用的机理。     

Synthesis and property studies of linear and kinked poly(pyreneethynylene)s

A series of fluorescent conjugated polymers, poly(pyreneethynylene)s, have been designed and synthesized to investigate the effect of shape of polymer backbone on physical properties. Polymers with linear and kinked backbone were synthesized using 1,6- and 1,8-disubstituted pyrene. The target copolymers were designed to incorporate various spacer units, such as, alkoxyphenyl, carbazole and fluorene on the polymer backbone. Characterization of the target compounds was achieved by NMR, IR, GPC and MALDI-TOF mass spectrometry. Detailed investigation on their optical, electrochemical and thermal properties revealed significant contribution of the geometry of polymer backbone towards physical properties. Kinked backbone of cisoid-polymers was found to result in lower optical band gap, less negative E_HOMO and higher thermal stability as compared to their linear analogues, most probably due to the coiling of polymer chains. Comparison of the physical properties of the polymers with those of the model compounds suggested similar extent of conjugation through 1,6- and 1,8-position of pyrene.