Efficient synthesis of an aldehyde‐capped polythiophene containing fluorinated electron‐withdrawing groups

To incorporate an acceptor type polythiophene segment onto a supramolecular block copolymer for potential light harvesting applications, effective synthetic routes for the end‐functionalized and acceptor‐substituted polythiophenes are critical. The Ullmann coupling reaction can be utilized to obtain electron‐deficient polythiophenes and to attach terminal thiophene units that carry functional groups. In this article, the reactions involving a 2,5‐dibromothiophene monomer containing an electron‐withdrawing fluorinated ester and 5‐bromo‐2‐thiophenecarboxaldehyde (the end‐capper) were studied in detail. It was found that the Ullmann coupling reaction of the dibromide is very fast (completed in a few minutes) and the terminal bromine group does not survive long under the reaction condition. These findings lead to the development of an effective procedure for aldehyde end‐capping of electron‐deficient polythiophenes. Polymers with molecular weights around 4000 Da are routinely obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 41–47, 2007     

Wavelength dependence in photochemical vapor deposition of aluminum film using dimethylaluminum hydride

In photochemical vapor deposition of aluminum film on silicon using dimethylaluminum hydride, (CH₃)₂AlH, a surface reaction dominated below a (CH₃)₂AlH pressure of 0.3 m Torr at 200°C, which was induced only with the 160 nm band emitted from a deuterium lamp. A gas-phase reaction occurred above 0.3 mTorr at 200°C, which could be induced by both 160 nm and 240 nm emission bands from the lamp. To distinguish between surface ad gas-phase reactions, a thickness profile was used. At 240°C the surface reaction could be induced even by the 240 nm band, while the deposits formed under illumination of the two bands were thinner than those obtained with only the 240 nm band, indicating occurrence of vacuum ultraviolet (VUV)-enhanced desorption. The mechanism responsible for the observed wavelength dependence in unclear. The electrical resistivity of the films deposited at 200°C was 4.5 μΩ cm, which did not change with wavelength.     

Matrix effects in the determination of butyltin compounds in environmental samples by GC AA after hydride generation

Experiments for the determination of mono-, di and tri-butyltin (MBT, DBT and TBT) by hydride generation/gas chromatography/atomic absorption spectrometry in various matrices (sediment, suspended matter, mussel, algae and water) have revealed that poor butyltin recoveries are obtained in sediments displaying high sulphur and hydrocarbon contents; very poor recoveries were also observed for TBT in sediments with high chlorophyll pigment contents as well as in algal samples. It was however not clear whether the hydride generatin was inhibited by these infering compounds, as was previously assumed in the case of hydrocarbons, or whether interferences affected the atomization rate. Further studies were performed to solve this problem in order to validate this method in the case of analyses of, for example, oil-contaminated sediment and algae. This paper presents the results obtained. It is concluded here that the poor recoveries were due to an inhibition of hydride generation rather than to interference at the atomization stage.     

Synthesis of self‐photosensitizing polyesters containing donor–acceptor norbornadiene moieties and benzophenone groups and their photochemical reactions

The ring‐opening copolymerization of a glycidyl ester derivative having a benzophenone group and the donor–acceptor norbornadiene (D‐A NBD) dicarboxylic acid, 5‐(4‐methoxyphenyl)‐1,4,6,7,7‐pentamethyl‐2,5‐norbornadiene‐2,3‐dicarboxylic acid, monoglycidyl ester derivatives with D‐A NBD dicarboxylic anhydride using tetraphenylphosphonium bromide as a catalyst proceeded smoothly to give novel self‐photosensitizing NBD polymers in good yields. The molecular weight of these polyesters was about 4,000, and lower than that of analogous NBD polymers having no benzophenone group. All the synthesized NBD polymers isomerized smoothly to the corresponding quadricyclane (QC) polymers upon UV irradiation in tetrahydrofuran (THF) solution and in the film state. The rate of the photoisomerization of the D‐A NBD moieties in these polymers was higher than that of the D‐A NBD moieties in the polymer having no photosensitizing group. Furthermore, the rate of the photoisomerization of the D‐A NBD moieties in these polymers was also higher than that of the NBD polymer with low molecular weight photosensitizer in dilute solution. The photo‐irradiated polymers having QC moieties released thermal energies of 146–180 J/g. The D‐A NBD moieties contained in these NBD polymers possessed fair to good fatigue resistance. The degradation of the NBD moieties in these polymers was 15–30% after 50 repeated cycles of interconversion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2978–2988, 2007     

Orbital correlation effects: The independent pair-potential approximation with application to the ground state and first ionized state of boron hydride

A new method is proposed for calculating correlation effects in atomic and molecular systems. The basis of the method is the formulation of a set of partial configuration expansions which yield directly variational orbital correlation corrections which are appropriately summed in order to obtain an estimate of the total correlation energy. This method is applied to the ground state of boron hydride and its cation at the equilibrium distance of BH. The results of the method are compared in detail with independent electron pair results and second order CI results. It is further shown that multiple substitutions are approximately accounted for in this method and the extent to which they are included is compared with other approximations. Finally, three methods of increasing accuracy, aimed at reducing the necessary computational effort, are given for determining the vertical ionization potential. The most economical method yields an IP of 9.70 eV or 0.03 eV less than the experimental IP. Completion of the basis is estimated to improve this value to 9.77 eV.     

On the determination of polarity parameters of silica by means of solvatochromic probe dyes

Empirical solvent parameters of silica surfaces are determined by means of solvatochromic dyes, e.g., Cu(tmen) (acac)⁺ ClO ₄ ^– /B(C₆H₅) ₄ ^– , Fe(phen)₂(CN)₂, and Michlers Ketone dissolved in 1,2-dichloroethane or cyclohexane. The values obtained by UV/VIS-measurements are compared with both the polarity scales of Kamlet and Taft and with Gutmann's donor and acceptor numbers. Kamlet and Taft's -parameter (the hydrogen-bond donation capacity of a solvent) is determined independently by means of salicylideneaniline. The ^* of silica is determined using 5-N,N-dimethylamino-5-nitro-2,2-bithiophene and the complex of tetracyanoethylene with Michlers Ketone, respectively. Further on the reliabilities of the obtained Kamlet-Taft parameters , , and ^* are checked by comparism with experimental and calculated values of theE _T(30)-parameter of silica by means of multi-parameter regression analysis. The surface properties of silica are influenced mainly by HBD-properties (75%) and dipolarity/polarizability ^* (20%), but hardly by the HBA-properties (<5%). UV/VIS-measurements were carried out in a special equipment with glass fiber optics, A drawing of the apparatus is given.     

Pseudo-Binary Phase Diagram of LiNH2-MH (M = Na,K) Eutectic Mixture

The hunt for a cleaner energy carrier leads us to consider a source that produces no toxic byproducts. One of the targeted alternatives in this approach is hydrogen energy, which, unfortunately, suffers from a lack of efficient storage media. Solid-state hydrogen absorption systems, such as lithium amide (LiNH₂) systems, may store up to 6.5 weight percent hydrogen. However, the temperature of hydrogenation and dehydrogenation is too high for practical use. Various molar ratios of LiNH₂ with sodium hydride (NaH) and potassium hydride (KH) have been explored in this paper. The temperature of hydrogenation for LiNH₂ combined with KH and NaH was found to be substantially lower than the temperature of individual LiNH₂. This lower temperature operation of both LiNH₂-NaH and LiNH₂-KH systems was investigated in depth, and the eutectic melting phenomenon was observed. Systematic thermal studies of this amide-hydride system in different compositions were carried out, which enabled the plotting of a pseudo-binary phase diagram. The occurrence of eutectic interaction increased atomic mobility, which resulted in the kinetic modification followed by an increase in the reactivity of two materials. For these eutectic compositions, i.e., 0.15LiNH₂-0.85NaH and 0.25LiNH₂-0.75KH, the lowest melting temperature was found to be 307 °C and 235 °C, respectively. Morphological studies were used to investigate and present the detailed mechanism linked with this phenomenon.     

Benzothiadiazole-based Conjugated Polymers for Organic Solar Cells

Benzothiadiazole(BT) is an electron-deficient unit with fused aromatic core, which can be used to construct conjugated polymers for application in organic solar cells(OSCs). In the past twenty years, huge numbers of conjugated polymers based on BT unit have been developed,focusing on the backbone engineering(such as by using different copolymerized building blocks), side chain engineering(such as by using linear or branch side units), using heteroatoms(such as F, O and S atoms, and CN group), etc. These modifications enable BT-polymers to exhibit distinct absorption spectra(with onset varied from 600 nm to 1000 nm), different frontier energy levels and crystallinities. As a consequence, BT-polymers have gained much attention in recent years, and can be simultaneously used as electron donor and electron acceptor in OSCs, providing the power conversion efficiencies(PCEs) over 18% and 14% in non-fullerene and all-polymer OSCs. In this article, we provide an overview of BTpolymers for OSCs, from donor to acceptor, via selecting some typical BT-polymers in different periods. We hope that the summary in this article can invoke the interest to study the BT-polymers toward high performance OSCs, especially with thick active layers that can be potentially used in large-area devices.