The optical, structural, and electrical properties of thin layers made from poly(3‐hexylthiophene) (P3HT) samples of different molecular weights are presented. As reported in a previous paper by Kline et al., Adv. Mater. 2003, 15, 1519, the mobilities of these layers are a strong function of the molecular weight, with the largest mobility found for the largest molecular weight. Atomic force microscopy studies reveal a complex polycrystalline morphology which changes considerably upon annealing. X‐ray studies show the occurrence of a layered phase for all P3HT fractions, especially after annealing at 150 °C. However, there is no clear correlation between the differences in the transport properties and the data from structural investigations. In order to reveal the processes limiting the mobility in these layers, the transistor properties were investigated as a function of temperature. The mobility decreases continuously with increasing temperatures; with the same trend pronounced thermochromic effects of the P3HT films occur. Apparently, the polymer chains adopt a more twisted, disordered conformation at higher temperatures, leading to interchain transport barriers. We conclude that the backbone conformation of the majority of the bulk material rather than the crystallinity of the layer is the most crucial parameter controlling the charge transport in these P3HT layers. This interpretation is supported by the significant blue‐shift of the solid‐state absorption spectra with decreasing molecular weight, which is indicative of a larger distortion of the P3HT backbone in the low‐molecular weight P3HT layers.
The first asymmetric organocatalytic epoxidation of alpha,beta-unsaturated aldehydes is presented. A chiral bisaryl-silyl-protected pyrrolidine acts as a very selective epoxidation organocatalyst using simple oxidation agents, such as hydrogen peroxide and tert-butyl hydroperoxide. The asymmetric epoxidation reactions proceed under environmental friendly reaction condition in, for example, water mixtures of alcohols, and the scope of the reaction is demonstrated by the formation of optically active alpha,beta-epoxy aldehydes in high yields and enantioselectivities >94% ee. Furthermore, the direct synthesis of the sex pheromone from an acaric mite by asymmetric epoxidation of citral is presented.
L‐Proline as the catalyst: The first direct asymmetric α‐amination of aldehydes using L‐proline as the catalyst is presented (see scheme; Pg=protecting group). This new reaction gives easy access to optically active α‐amino aldehydes, α‐amino alcohols, and α‐amino acids from simple and easily available starting materials and catalysts. The reactions proceed in high yields and excellent enantioselectivities with as little as 2 mol % of the catalyst.
The first direct catalytic asymmetric alpha-amination of ketones catalyzed by l-proline has been developed. The reactions proceed with various azodicarboxylates as the nitrogen source in high yields and excellent enantioselectivities (up to 99% ee). The scope and potential of the reaction are demonstrated by further transformation of the alpha-hydrazino ketones formed to both optically active syn and anti-alpha-amino alcohol derivatives.
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