Naphthodithiophene-2,1,3-benzothiadiazole copolymers for bulk heterojunction solar cells

Two newly synthesized naphthodithiophene-based copolymers, PNB, exhibit a low optical bandgap of ～1.64 eV with which the solar cells fabricated from the blend of PNB and PC(71)BM afforded a power conversion efficiency of 5.3% with external quantum efficiency over 60% in a broad spectral range.     

The unimolecular dissociation of 3,4-dihydro-2H-pyran over a wide temperature range

The thermal decomposition of 3,4-dihydro-2H-pyran (DHP, C₅H₈O) has been investigated by two methods: in shock waves with the laser-schlieren technique using mixtures of 5 and 10% DHP in krypton over 900–1500 K, 110–560 torr; in a flow tube having a reaction pressure 0.5 torr above atmospheric using the decomposition of allylethyl ether as an internal standard, and covering 663–773 K. The retro-Diels-Alder dissociation to the stable acrolein and ethylene is the dominant channel for all conditions. Precise rate constants (rms deviation of 10%) were obtained for this process over the indicated temperature ranges. Unimolecular falloff is evident in the shock-tube results, and RRKM calculations also predict a slight falloff at the lower temperatures. These RRKM calculations use a routine vibration model transition state and agree closely with the high-temperature data when 〈ΔE〉_down is a fixed 400 cm^?1. Arrhenius expressions for k_∞ derived from the two measurements are in close accord and also consistent with most previous studies of this reaction. © 1995 John Wiley & Sons, Inc.     

A least-squares finite element method for time-dependent incompressible flows with thermal convection

The time-dependent Navier–Stokes equations and the energy balance equation for an incompressible, constant property fluid in the Boussinesq approximation are solved by a least-squares finite element method based on a velocity–pressure–vorticity–temperature–heat-flux ( u –P–ω–T– q ) formulation discretized by backward finite differencing in time. The discretization scheme leads to the minimization of the residual in the l²-norm for each time step. Isoparametric bilinear quadrilateral elements and reduced integration are employed. Three examples, thermally driven cavity flow at Rayleigh numbers up to 10⁶, lid-driven cavity flow at Reynolds numbers up to 10⁴ and flow over a square obstacle at Reynolds number 200, are presented to validate the method.     

Isotopic compositions and scalings

We review experimental and theoretical studies devoted to extract information on the behaviour of the symmetry energy, in density regions different from the normal value, with charge-asymmetric reactions at Fermi energies. In particular, we focus on the analysis of fragmentation reactions and isotopic properties of the reaction products. Results concerning “isoscaling” properties and the N/Z equilibration among the reaction partners in semi-peripheral reactions are also discussed.     

Comparison between experimental and calculated results on the decomposition of chemically activated alcohols

The life times of chemically activated alcohols have been determined using the high-pressure unimolecular rate parameters for thermal decomposition of alcohols from shocktube studies and RRKM calculations. They are compared with literature numbers (from insertion of 0(¹D) into hydrocarbons). It is suggested that in some cases singlet oxygen carries excess energy into the hydrocarbon. The consequences of such an assumption are explored and discrepancies with previously published conclusions discussed.     

Thermal decomposition of 3,4-dimethylpentene-1, 2,3,3-trimethylpentane, 3,3-dimethylpentane,and isobutylbenzene in a single pulse shock tube

Several hydrocarbons have been pyrolyzed in a single pulse shock tube. Rate parameters for the main bond breaking step have been found to be In combination with similar studies carried out earlier and through application of the well-established experimental rule (k(AB)/k_r(AA)k_r(BB))^1/2 ～ 2 where A and B are radicals and the rate constants are for the combination of these radicals, rate parameters for the thermal decomposition of all the hydrocarbons formed from any pair of the following radicals: methyl, ethyl, isopropyl, t-butyl, t-amyl, allyl, methylallyl, and benzyl have been calculated. The available calculated and experimental values of the decomposition rate constants are in excellent agreement. It appears that, with the possible exception of reactions involving the ejection of methyl radicals, the frequency factors per bond are nearly constant, depending only upon the type of carbon–carbon bond that is being broken. These values are all lower than those expected from the radical recombination rates. Heats of formation of ethyl, t-amyl, benzyl, methylallyl, n-propyl, s-butyl, isobutyl, neopentyl, and 3-pentyl radicals have been derived. Rate parameters for the decomposition of some simple ketones and ethers have also been estimated.     

Striking contrasts in stereoselectivities of spiro-claisen rearrangements of pyranosides versus carbocycles.

Structurally equivalent derivatives of pyranosides and cyclohexanes undergo the spiro-Claisen rearrangement with different stereochemical results. A rationalization for the course observed with the pyranosides is suggested, which invokes interaction of the oxygen lone pair with a (developing) electron deficient centre at the spiro carbon.     

Raman spectroscopy of intercalated layered structure compounds

The Raman spectra of intercalated 1TTaS₂ and 2HTaSe₂ have been measured for the first time. Normal symmetry allowed optic phonons and charge density wave induced modes are observed in both systems. The spectra of the ethylenediamine intercalated compounds are qualitatively similar to those of the pure materials with small quantitative shifts in frequency and changes in the relative intensities of the CDW induced modes. The qualitative similarities in the spectra of the pure and the intercalated compounds reflect the two dimensional character of these materials and show that the dynamic properties of the charge density wave states are largely determined by intralayer effects.