Facile synthesis and high optical activity of poly(1‐pentyne)s carrying amino‐acid pendant groups

1‐Pentynes containing different amino acid moieties and pendant terminal groups {HC?C(CH₂)₂CONHC(R′)HCO₂CH₃, where R′ = CH₃, CH₂CH(CH₃)₂, CH₂C₆H₅, and HC?C(CH₂)₂CONHC[CH₂CH(CH₂)₃]HCO₂‐(1R,2S,5R)‐(+)‐menthol} have been designed and synthesized. The polymerizations of the monomers are effected by organorhodium catalysts, giving soluble polymers with moderate molecular weights in satisfactory yields. The structures and properties of the polymers have been characterized and evaluated with infrared, nuclear magnetic resonance, thermogravimetric analysis, circular dichroism, and ultraviolet analyses. All the polymers are thermally stable (≥300 °C) and show strong circular dichroism signals at ～310 nm because of the helicity of the polyene backbone. The circular dichroism and ultraviolet absorptions of the polymers can be tuned with a solvent. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6190–6201, 2006     

Synthesis and properties of poly(1-phenyl-1-octyne)s containing stereogenic and chromophoric pendant groups

Poly(1-phenyl-1-octyne)s containing different stereogenic and chromophoric pendants {-[(C6H13)C=C(C6H4-p-CO2-R)]n-R=[(1S)-endo]-(-)-borneyl (P3), (1R,2S,5R)-(-)-menthyl (P4),―C6H4-p-(1R,2S,5R)-(-)-menthyl (P5), 2-napthyl (P6), 4-biphenylyl (P7)} have been designed and synthesized. The polymers are prepared in moderate yields by WCl6-Ph4Sn and possess high molecular weights (Mw up to 64000). The structures and properties of the polymers are characterized and evaluated by NMR, TGA, UV, CD, PL, and EL analyses...     

5-[4′-正庚基-氧-联苯基-4-氧-羰基]基-1-正戊炔的晶体结构研究

由于共轭聚合物的光致发光和电致发光性能,有望成为制造全塑性发光二极管的材料,因此近年来已引起人们的研究兴趣[1].聚乙炔是一种典型的共轭聚合物,其不稳定性和难加工性限制了它的应用.而含联苯液晶基元的取代聚乙炔,不仅其难加工性得到了改善,提高了稳定性,而且赋予了聚合物液晶性,因此有望开发出一批新型的高性能材料[2].目前对这类新型取代乙炔聚合物及其单体的凝聚态结构的报道还较少.本文通过WAXD,TEM和AFM等手段对小分子液晶5-[4′-正庚基-氧-联苯基-4-氧-羰基]基-1-正戊炔(A3E′O7)的晶体结构进行了研究.1实验部分1.1样品及…     

Steric Effects on Reaction Rates – III. Application of Force-Field Calculations to Chromic Acid Oxidation of Alcohols

The rates of oxidation with chromic acid of 15 bi- and polycyclic secondary alcohols have been measured and correlated with strain changes calculated by the MM1-program between the alcohols and the corresponding ketones. A correlation of the same quality is obtained upon representation of OH-strain by CH₃-strain. The significance of the correlations with respect to the oxidation mechanism as well as the limitations of the applicability of force-field calculations to reactivity problems are discussed.     

Design of a lattice-matched III–V–N/Si photovoltaic tandem cell monolithically integrated on silicon substrate

In this paper, we present a comprehensive study of high efficiencies tandem solar cells monolithically grown on a silicon substrate using GaAsPN absorber layer. InGaAs(N) quantum dots and GaAsPN quantum wells have been grown recently on GaP/Si susbstrate for applications related to light emission. For photovoltaic applications, we consider the GaAsPN diluted nitride alloy as the top junction material due to both its perfect lattice matching with Si and ideal bandgap energy for current generation in association with the Si bottom cell. Numerical simulation of the top cell is performed. The effect of layer thicknesses and doping on the cell efficiency are evidenced. In these structures a tunnel junction (TJ) is needed to interconnect both the top and bottom sub-cells. We compare the simulated performances of different TJ structures and show that the GaP(n+)/Si(p+) TJ is promising to improve performances of the current–voltage characteristic.     

Aggregation‐Induced Emission of Tetraphenylethene–Hexaphenylbenzene Adducts: Effects of Twisting Amplitude and Steric Hindrance on Light Emission of Nonplanar Fluorogens

A series of nonplanar tetraphenylethene (TPE)–hexaphenylbenzene (HPB) adducts was designed and synthesized by Diels–Alder reaction of the acetylene precursors and tetraphenylcyclopentadienone. All of the adducts showed aggregation‐induced emission features. The twisting amplitude and steric hindrance of the TPE and HPB units were found to play a crucial role in their fluorescence behaviors in the aggregated state.     

Taking one charge off a two-dimensional Wigner crystal

A planar array of identical charges at vanishing temperature forms a Wigner crystal with hexagonal symmetry. We take off one (reference) charge in a perpendicular direction, hold it fixed, and search for the ground state of the whole system. The planar projection of the reference charge should then evolve from a sixfold coordination (centre of a hexagon) for small distances to a threefold arrangement (centre of a triangle), at large distances d from the plane. The aim of this paper is to describe the corresponding non-trivial lattice transformation. For that purpose, two numerical methods (direct energy minimisation and Monte Carlo simulations), together with an analytical treatment, are presented. Our results indicate that the d = 0 and d → ∞ limiting cases extend for finite values of d from the respective starting points into two sequences of stable states, with intersecting energies at some value d_t; beyond this value the branches continue as metastable states.     

Hydration of nitriles: an examination in terms of No Barrier Theory

Nitriles pose an interesting problem to the explanatory powers of organic chemistry because, despite the favorable overall thermodynamics of hydrolysis to the corresponding amides, the reactions are inherently slow. The rate determining step is hydration of the nitrile to give the imidic acid, which quickly tautomerizes to the amide. In terms of Marcus Theory, the intrinsic barriers for acid and base‐catalyzed hydration are higher for nitriles than for amides, which are themselves slow reactions. It is remarkable that hydration of a nitrile, for which the free energy change is close to zero except for polyhaloacetonitriles, is much slower than hydration of an amide, which is energetically unfavorable. This can be explained by No Barrier Theory in terms of the high energetic cost of the geometrical distortions in “one thing at a time” corner species. There are no experimental equilibrium constants for this initial hydration step, so we have determined them computationally. The free energy change for the initial hydration is small; it is the fast and energetically downhill second step, tautomerization to the amide, which makes the overall hydrolysis of nitrile to amide thermodynamically favorable. Very few of the pK_a values needed in the acid and base‐catalyzed mechanisms are known, so we used linear free energy relations and treat the parent pK_a values as adjustable parameters. This procedure leads to pK_a values in accord with expectation based on such data as are available and permits calculation of rate constants in satisfactory agreement with experiment. Copyright © 2013 John Wiley & Sons, Ltd.