Regiorandom polymers

Similar thermochromic and solvatochromic effects have been observed by Bidan and coworkers71 for the optically active polymer 25 prepared in a regiospecihc fashion (100% HT-HT coupling) by the McCullough method. In contrast, the analogous regiorandom polymer prepared by oxidation with FeCl3 in chloroform has only weak optical activity. However, the disubstituted chiral polythiophene 26, synthesized by... 

NEXAFS orientation analysis can also be applied to polymer semiconductors, hi this example, films of regioregular and regiorandom P3HT were spin-coated from chloroform to approximately 20 mn atop the native oxide of silicon, then melted at 250°C and slowly cooled under vacuum. NEXAFS carbon K-edge spectra were collected at the same conditions as for pentacene. The resultant spectra are shown in Figure 4.2.7(a-b). 

The position of the emission maximum (575 nm) is indistinguishable in HHTT and HT polymers, while Yamamoto s regiorandom polymer of the same constitution (16a) shows emission maxima at 529 and 558 nm in the solid state. Again, solid-state ordering must be the explanation for these differences in emissive behavior. 

Changing the structure of the polymer from regioregular to regio-random significantly accelerates the degradation, probably due to the higher triplet yield of the regiorandom polymer. 

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