Strong stacking behavior and large third-order nonlinear optical susceptibility χ(3) of head-to-head-type poly(3-alkynylthiophene-2,5-diyl), HH-P3(CCR)Th

The head-to-head-type poly(3-alkynylthiophene-2,5-diyl) HH-P3(CCR)Th has been shown to exhibit a strong tendency to self-assemble. The UV–vis spectrum of HH-P3(CCDec)Th (Dec = decyl) in 1,2-dichlorobenzene at 131 °C showed a peak at λmax = 520 nm, which shifted to λmax = 553 nm at 25 °C, with a shoulder peak at 608 nm. However, the UV–vis spectrum of an HH-P3(CCDec)Th film showed a more pronounced shift in its UV–vis absorption peak to a longer wavelength. These phenomena are the characteristics of the self-assembly of the polymer molecule. The HH-P3(CCDec)Th film had a large third-order nonlinear optical susceptibility χ(3) of 3.6 × 10−11 esu.