Thieno[3,4-b]pyrazines and their applications to low band gap organic materials

The application of fused-ring thieno[3,4-b]pyrazines in conjugated organic polymers has been found to be a powerful approach to the production of low band gap materials. While thieno[3,4-b]pyrazine-based materials date back to the early 1990s, significant advances in the preparation and scope of thieno[3,4-b]pyrazine-based materials have been reported in recent years, primarily in response to the increasing demand for reduced band gap materials in photovoltaic devices. In this review, we provide an overview of thieno[3,4-b]pyrazines and their application to conjugated materials, highlighting in particular the recent advances in the breadth of thieno[3,4-b]pyrazine building blocks and the promise of tuning materials to achieve optimal properties for specific applications.     

The application of mode coupling theory to the transmission of sound in the sidebranch of a rectangular duct system

Mode coupling is applied to rectangular ducts of the size encountered in modern ventilation systems. Theory is developed to describe the transmission of sound along a straight duct, and along a sidebranch. Acoustic impedance boundary conditions at the duct walls are included. Experimental and predicted results are presented for the frequency spectra, cross-sectional variation and longitudinal variation in the entry and sidebranch ducts caused by a pure tone source. Good agreement is shown between the two sets of results.     

Analysis of the Rayleigh-Plesset equation with chirp excitation

The case of a bubble being insonified by an ultrasonic excitationin the form of a linear chirp is considered here. The dynamicalequation of the bubble's motion is solved analytically and comparedto a numerical solution. The analytical solution is then usedto investigate the problem of maximizing the amplitude of thesecond harmonic with respect to the various system and signalparameters.     

Pyrolytic hydrocarbon growth from cyclopentadiene

Aromatic hydrocarbon growth from cyclopentadiene (CPD) was studied using a laminar flow reactor operating in the temperature range 550-950 °C without oxygen. Benzene, indene, and naphthalene were the major products, which is in agreement with the previous computational studies on the reaction pathways from CPD. A crossover of indene and naphthalene yields around 775 °C was also observed, which further supports the results of the computational studies. Although the specific intermediates in the proposed pathways from CPD were not detected, the high selectivity of products and the observation of other methylindene and dihydronaphthalene intermediates suggest that the recombination of two CPDs via radical-molecule and/or radical-radical pathways to form indene and naphthalene is the dominant formation pathway. In addition to the products from the CPD-CPD reactions, the products from the reactions of CPD with indene, naphthalene, and acenaphthylene were also observed, which demonstrate the importance of CPD in carbon growth.     

Electronic structure of compound I in human isoforms of cytochrome P450 from QM/MM modeling

Human cytochromes P450 play a vital role in drug metabolism. The key step in substrate oxidation involves hydrogen atom abstraction or C=C bond addition by the oxygen atom of the Compound I intermediate. The latter has three unpaired electrons, two on the Fe-O center and one shared between the porphyrin ring and the proximal cysteinyl sulfur atom. Changes in its electronic structure have been suggested to affect reactivity. The electronic and geometric structure of Compound I in three important human subfamilies of cytochrome P450 (P450, 2C, 2B, and 3A) that are major contributors to drug metabolism is characterized here using combined quantum mechanical/molecular mechanical (QM/MM) calculations at the B3LYP:CHARMM27 level. Compound I is remarkably similar in all isoforms, with the third unpaired electron located mainly on the porphyrin ring, and this prediction is not very sensitive to details of the QM/MM methodology, such as the DFT functional, the basis set, or the size of the QM region. The presence of substrate also has no effect. The main source of variability in spin density on the cysteinyl sulfur (from 26 to 50%) is the details of the system setup, such as the starting protein geometry used for QM/MM minimization. This conformational effect is larger than the differences between human isoforms, which are therefore not distinguishable on electronic grounds, so it is unlikely that observed large differences in substrate selectivity can be explained to a large extent in these terms.     

Some observations on employing a panel's cill and reveal to enhance noise reduction

The cill and reveal of a panel or window are known to influence the Normalised Noise Reduction. Reported here are additional observations upon their effect which may be employed to increase the sound insulation of rooms within the built environment.     

A theoretical investigation of chirp insonification of ultrasound contrast agents

A theoretical investigation of second harmonic imaging of an Ultrasound Contrast Agent (UCA) under chirp insonification is considered. By solving the UCA’s dynamical equation analytically, the effect that the chirp signal parameters and the UCA shell parameters have on the amplitude of the second harmonic frequency are examined. This allows optimal parameter values to be identified which maximise the UCA’s second harmonic response. A relationship is found for the chirp parameters which ensures that a signal can be designed to resonate a UCA for a given set of shell parameters. It is also shown that the shell thickness, shell viscosity and shell elasticity parameter should be as small as realistically possible in order to maximise the second harmonic amplitude. Keller-Herring, Second Harmonic, Chirp, Ultrasound Contrast Agent.     

Synthesis and photovoltaic performance of donor–acceptor polymers containing benzo[1,2‐b:4,5‐b′]dithiophene with thienyl substituents

Three alternating donor–acceptor copolymers have been synthesized by Stille coupling polymerization of 2,6‐(trimethyltin)?4,8‐bis(5‐dodecylthiophene‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene with 1,3‐dibromo‐5‐hexylthieno[3,4‐c]pyrrole‐4,6‐dione, 4,7‐dibromo‐1,3‐benzothiadiazole, and 5,7‐dibromo‐2,3‐didodecylthieno[3,4‐b]pyrazine, respectively. The synthesized polymers were tested in bulk heterojunction solar cells as blends with the acceptor [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM). The thienopyrroledione copolymer displayed a power conversion efficiency of 3.00% which was increased to 3.86% by application of the additive 1,8‐diiodooctane (DIO). Tapping mode atomic force microscopy analysis indicated that there was an increase in the phase separation between polymer and PCBM, leading to an improvement in the performance upon the addition of DIO. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2622–2630