Fluorene‐based alternating polymers containing electron‐withdrawing bithiazole units: Preparation and device applications

We report here the synthesis via Suzuki polymerization of two novel alternating polymers containing 9,9‐dioctylfluorene and electron‐withdrawing 4,4′‐dihexyl‐2,2′‐bithiazole moieties, poly[(4,4′‐dihexyl‐2,2′‐bithiazole‐5,5′‐diyl)‐alt‐(9,9‐dioctylfluorene‐2,7‐diyl)] (PHBTzF) and poly[(5,5′‐bis(2″‐thienyl)‐4,4′‐dihexyl‐2,2′‐bithiazole‐5″,5″‐diyl)‐alt‐(9,9‐dioctylfluorene‐2,7‐diyl)] (PTHBTzTF), and their application to electronic devices. The ultraviolet–visible absorption maxima of films of PHBTzF and PTHBTzTF were 413 and 471 nm, respectively, and the photoluminescence maxima were 513 and 590 nm, respectively. Cyclic voltammetry experiment showed an improvement in the n‐doping stability of the polymers and a reduction of their lowest unoccupied molecular orbital energy levels as a result of bithiazole in the polymers' main chain. The highest occupied molecular orbital energy levels of the polymers were ?5.85 eV for PHBTzF and ?5.53 eV for PTHBTzTF. Conventional polymeric light‐emitting‐diode devices were fabricated in the ITO/PEDOT:PSS/polymer/Ca/Al configuration [where ITO is indium tin oxide and PEDOT:PSS is poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonic acid)] with the two polymers as emitting layers. The PHBTzF device exhibited a maximum luminance of 210 cd/m² and a turn‐on voltage of 9.4 V, whereas the PTHBTzTF device exhibited a maximum luminance of 1840 cd/m² and a turn‐on voltage of 5.4 V. In addition, a preliminary organic solar‐cell device with the ITO/PEDOT:PSS/(PTHBTzTF + C₆₀)/Ca/Al configuration (where C₆₀ is fullerene) was also fabricated. Under 100 mW/cm² of air mass 1.5 white‐light illumination, the device produced an open‐circuit voltage of 0.76 V and a short‐circuit current of 1.70 mA/cm². The fill factor of the device was 0.40, and the power conversion efficiency was 0.52%. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1845–1857, 2005     

Preliminary study to prepare a reference material of styrene metabolites – mandelic acid and phenylglyoxylic acid – in human urine

 A preliminary batch of the reference material was prepared by freeze-drying pooled urine samples obtained from healthy persons occupationally exposed to styrene. Tests for homogeneity and stability were performed by determining urine concentrations of mandelic (MA) and phenylglyoxylic acids (PGA). The urinary MA and PGA concentrations were followed over an 8-month period using high performance liquid chromatography (HPLC). No changes of the concentration values were found. Pure PA and PGA from Merck and Fluka, respectively, were used for traceability purposes, because certified or standard reference materials for MA and PGA do not exist. Control material ClinChek-Urine Control (Recipe) was analysed simultaneously. The mean values of MA and PGA compared well with the means of control samples and fell within the control range. The certified values and their uncertainties were evaluated from the results of interlaboratory comparisons, homogeneity (277.0 ± 7.4 mg L⁻¹ for MA and 148.0 ± 4.7 mg L⁻¹ for FGA) and stability tests. The values are unweighted arithmetical averages of accepted results and their uncertainties are combined uncertainties enlarged by coefficient k=1, evaluated from the standard uncertainties of the interlaboratory comparison, homogeneity and stability tests. Received: 17 September 2002 Accepted: 1 November 2002 Acknowledgement This work was supported by the Internal Grant Agency of Ministry of Health of the Czech Republic (Grant NJ/6784–3). Presented at CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia Correspondence to I. Šperlingová     

Two photon-induced fluorescence intensity and anisotropy decays of diphenylhexatriene in solvents and lipid bilayers

We measured the fluorescence intensity and anisotropy decays of 1,6-diphenyl-1,3,5-hexatriene (DPH)-labeled membranes resulting from simultaneous two-photon excitation of fluorescence. Comparison of these two-photon data with the more usual one-photon measurements revealed that DPH displayed identical intensity decays, anisotropy decays, and order parameters for one- and two-photon excitation. While the anisotropy data are numerically distinct, they can be compared by use of the factor 10/7, which accounts for the two-photon versus one-photon photoselection. The increased time 0 anisotropy of DPH can result in increased resolution of complex anisotropy decays. Global analysis of the one- and two-photon data reveals consistency with a single apparent angle between the absorption and the emission oscillators. The global anisotropy analysis also suggests that, except for the photoselection factor, the anisotropy decays are the same for one-and two-photon excitation. This ideal behavior of DPH as a two-photon absorber, and its high two-photon cross section, makes DPH a potential probe for confocal two-photon microscopy and other systems where it is advantageous to use long-wavelength (680- to 760-nm) excitation.     

Preparation of a reference material “Creatinine in Human Urine”

Two batches of a reference material “Creatinine in Human Urine” have been prepared with creatinine concentrations at the physiological level, and used in interlaboratory comparisons in which up to 26 laboratories participated employing up to 4 independent methods. The 95% confidence intervals obtained for the certified creatinine concentrations are better than the “acceptable ranges” of commercially control samples available for clinical laboratories, the certified values being traceable to mean values of the commercial control samples. Thus, a suitable reference material has been prepared for the quality assurance of environmental and occupational health studies in which the concentration of a pollutant or its metabolites in human urine has to be related to the creatinine concentration.     

Classical and quantum chaos for a kicked top

We discuss a top undergoing constant precession around a magnetic field and suffering a periodic sequence of impulsive nonlinear kicks. The squared angular momentum being a constant of the motion the quantum dynamics takes place in a finite dimensional Hilbert space. We find a distinction between regular and irregular behavior for times exceeding the quantum mechanical quasiperiod at which classical behavior, whether chaotic or regular, has died out in quantum means. The degree of level repulsion depends on whether or not the top is endowed with a generalized time reversal invariance.     

Morphology,structure, and photoactivity of two types of graphene oxide-TiO<Subscript>2</Subscript> composites

Two types of graphene oxide-TiO₂ composites were prepared: one by including graphene oxide flakes in the TiO₂ sol, followed by thermal treatment (GI composite) at 300°C, and the second by including graphene oxide flakes in the calcined (at 500°C) TiO₂ xerogel (GII composite). The composites were characterized by SEM, TEM-EDS, TEM-SADP, STEM-HAADF, HRTEM coupled with FT, XRD, and XPS. Photocatalysis results were fitted to different kinetic models (pseudo-first and pseudo-second kinetics, intraparticle Weber-Morris diffusion, film diffusion, and external mass transfer). The results showed that by introducing graphene oxide flakes in the TiO₂ sol, followed by thermal treatment at 300°C (GI composite), an efficient graphene oxide-TiO₂ catalyst with high specific surface area, heterogeneity, and many graphitized areas can be obtained. Complete crystallization of the composite is not the key issue for the best photoactivity achievement. The rate limiting step in the photocatalytic process is the photooxidation of SA molecules on the TiO₂ surface.     

An Approach to Transfer Methods from HPLC to UHPLC Techniques in Some Carbapenems

Stability-indicating LC methods were developed and validated for the quantitative determination of doripenem, meropenem and tebipenem in the presence of their degradation products formed during forced degradation studies. Isocratic HPLC and UHPLC separations were performed with a core–shell Kinetex 1.7, 2.6 and 5 µm, all C18, 100A, 100 × 2.1 mm columns and the mobile phase composed of acetonitrile and 12 mmol L⁻¹ ammonium acetate in different ratios. The flow rates of the mobile phase were: 0.5 mL min⁻¹ for 1.7 µm column, and 1.0 mL min⁻¹ for 2.6 and 5 µm ones. Detection wavelength was 298 nm and temperature was set at 30 °C. All analysed drugs were exposed to stress conditions which caused their hydrolysis and thermal degradation. The methods were validated by evaluation of linearity, accuracy, precision, selectivity and robustness. Proposed methods were successfully applied for the determination of investigated antibiotics during kinetic studies in aqueous solutions and in the solid state. The advantages of chromatographic procedures which are based on the use of C18 stationary phases with different particle sizes in the analysis of selected carbapenems were discussed.

     

Determination of As by instrumental neutron activation analysis in sectioned hair samples for forensic purposes: chronic or acute poisoning?

Autopsy of 29-year old woman suspicious of committing suicide by the ingestion of As₂O₃ yielded contradictory findings. All pathological findings as well as clinical symptoms suggested acute poisoning, while a highly elevated As level of 26.4 μg g⁻¹ in her hair collected at the autopsy, which was determined with inductively coupled plasma mass spectrometry indicated chronic poisoning. To elucidate this discrepancy, instrumental neutron activation analysis (INAA) with proven accuracy was performed of another set of sectioned hair samples. Levels of As found by INAA in the range of 0.16–0.26 μg g⁻¹ excluded chronic poisoning, because the person died after approximately 14 h after the As₂O₃ ingestion. Two reasons for the discordant As results obtained by ICP-MS and INAA are considered: (1) accidental, non-removed contamination of hair on the As₂O₃ ingestion; (2) erroneous performance of ICP-MS.     

Catalytic conversion of lactic acid into propylene glycol over various metals supported on silica

Catalytic hydrogenation of lactic acid to propylene glycol was performed over various metals (Ag, Co, Cu, Ni, Pt, and Ru) supported on silica prepared by an incipient wetness impregnation method. The loading amount of each metal was 5 wt%. Crystallinity of the synthesized catalysts was investigated by X-ray diffraction (XRD), and the BET method was utilized to examine the surface area. Pore volume and pore size of catalysts were determined using BJH analysis of the N₂ adsorption isotherm. Particle sizes of various metals were determined from transmission electron microscopy (TEM) images. The catalytic activity was found to be strongly dependent on the supported metal. Among catalysts tested, Ru/SiO₂ showed the highest propylene glycol yield. The yield of propylene glycol increased with pressure, and the highest yield was achieved at 130 °C.