3-octyloxy-4-methylthiophene

A two-phase thermochromic behavior, as in PDDT and poly(3-methyl-4-octyloxythiophene), is related to the formation of delocalized conformational defects upon heating. These defects are possible due to the presence of sterically demanding substituents between each consecutive repeating unit [330]. In the solid state at room temperature, PDDT and poly(3-octyloxy-4-methyl-thiophene) have a coplanar conformation for the main chain. Heating (25 to 150°C) increases the repulsive intrachain steric interactions and introduces some conformational disorder in the side groups, forcing the polymer backbone to adopt a nonplanar conformation [331, 332]. Temperature dependent UV/vis absorption measurements of fluorinated PTs, e.g., poly(3 -perfluorohexyl-2,2 5, 2"-terthiophene), poly[3-(pentadecafluorooctyloxy)-4-methylthiophene] and poly[3-(tridecafluorononyl)thiophene], show a blue shift of the maximum... 

Several examples of the aforementioned polyalkoxythiophenes and their doping/dedoping behavior have been described in more detail in the paper by Daoust and Leclerc. The color change in humid air parallels partial or complete dedoping of the tetrachloroferrates, observed with methanol. Whereas poly-3,4-dibutox5d hiophene is completely dedoped to the brown-red neutral state by contact with methanol, poly-3-butoxythiophene, poly-3-butoxythio-phene, poly-3-butoxy-4-methylthiophene, and poly-3-octyloxy-4-methylthio-phene remain partially doped under similar conditions with methanol. 

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