Synthesis and properties of carbazole‐layered polymers

New aromatic ring‐layered polymers consisting of carbazole as a layered aromatic group and xanthene as a scaffold were designed and synthesized via the Sonogashira–Hagihara coupling reaction. Their optical and electrochemical behaviors were investigated in detail; the results showed that these polymers could be used as hole‐transporting materials. Polymers with nitrobenzene moieties at the polymer chain ends quenched the emission from the layered carbazoles to the nitrobenzene termini; thus, the polymers acted as the molecular wire that transferred photoexcited energy and/or electrons to the polymer termini. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4279–4288, 2009     

Temperature‐dependent polymorphic crystalline structure and melting behavior of poly(butylene adipate) investigated by time‐resolved FTIR spectroscopy

The polymorphic crystalline structure and melting behavior of biodegradable poly(butylene adipate) (PBA) samples melt‐crystallized at different crystallization temperatures were studied by differential scanning calorimetry (DSC) and fourier transform infrared (FTIR) spectroscopy. The crystalline structure and melting behavior of PBA were found to be greatly dependent on the crystallization temperature. By comparison of the FTIR spectra and the corresponding second derivatives between the α‐ and β‐crystal of PBA, the spectral differences were identified for the IR bands appeared at 1485, 1271, 1183, and 930 cm^?1 and the possible reasons were presented. Especially, the 930 cm^?1 band was found to be a characteristic band for the β‐crystal. Combining the DSC data with the analysis of normalized intensity changes of several main IR bands during the melting process, the melting behaviors of the α‐ and β‐crystal were clarified in detail. It is demonstrated by the in situ IR measurement that the β‐crystalline phase would transform into the α‐crystalline phase during the melting process, and the solid–solid phase transition from the β‐ to α‐crystal was well elucidated by comparing the intensity changes of the 1170 and 930 cm^?1 bands. The dependence of the β‐ to α‐crystal phase transition on the heating rate was revealed by monitoring the intensity ratio of the 909 and 930 cm^?1 band. It was suggested that at the heating rate of 0.5 or 1 °C/min, the percent amount of the transformed α‐crystal from the β‐crystal was much higher than that at the higher heating rate. The β‐crystal transforms into the α‐crystal incompletely at the higher heating rate because of the less time available for the phase transition. In addition, the β‐ to α‐crystal phase transition was further confirmed by the IR band shifts during the melting process. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1997–2007, 2009     

Characterization of Full-WDM-Band Photodiode Modules Using Raman Amplifiers in the U Band at 40 Gb/s

We present the characteristics of a full-WDM-band photodiode module in 40 Gb/s U-band operation using a Raman amplifier. This module is suitable for wide-band transmission systems with the additional new channels in the U band.     

Weak order stochastic Runge–Kutta methods for commutative stochastic differential equations

A new explicit stochastic Runge–Kutta scheme of weak order 2 is proposed under a commutativity condition, which is derivative-free and which attains order 4 for ordinary differential equations. The weak order conditions are derived by utilizing multi-colored rooted tree analysis and a solution is found in a transparent way. The scheme is compared with other derivative-free and weak second order schemes in numerical experiments.     

Effect of surface compound formation on the photo-induced reaction at polycrystalline TiO2 semiconductor electrodes

The oxidation of methanol at the surface of illuminated polyerystalline TiO₂ semiconductor electrodes was investigated by measuring the current-doubling effect. Compounding TiO₂ with MoO₂ or MoS₂ increases the efficiency of alcohol oxidation. This compounding effect is discussed with reference to the electrode characteristics.     

Analysis of the hysteresis curve of ferroelectric polymers by a phenomenological relaxation theory

A simple relaxation theory for the displacement versus electric field hysteresis of ferroelectric polymers is developed in which the relaxation time is assumed to be a function of electric field, as has been experimentally evidenced by polarization-reversal switching. The theory gives an analytical expression for the hysteresis curve. The coercive field E_c predicted by the theory agrees well with data on E_c as a function of temperature for poly(vinylidene fluoride) from ?60 to 20°C and with data on E_c as a function of frequency for vinylidene fluoride/trifluoroethylene copolymer (73/27 molar ratio) at 20°C over the range 0.01–0.7 Hz.     

Excimer fluorescence of α,ω-biscarbazolylalkanes doped in polycarbonate

Fluorescence properties of biscarbazolyl compounds in polycarbonate have been examined. The intensity of excimer fluorescence progressively decreases for compounds in which two carbazole groups are bound by C₆, C₁₀, C₄, C₅ and C₃ methylene chains. It is determined that the intramolecular interaction dominates the excimer formation.