Alkylthio-functionalized Polymers Containing Alternating Phenylene and Thiophenediyl/Bithiophenediyl Repeating Units: the Synthesis and Characterization

Alkylthio(SR)-functionalized polymers poly(3-alkylthio-2,5-thiophenediyl-1,4-phenylene-alt-4-alkylthio-2,5-thiophenediyl-1,4-phenylene) (P1, alkyl = butyl, octyl and dodecyl) and poly[4,4ʹ-bis(alkylthio)-2,2ʹ-bithiophene-5,5ʹ-diyl-alt-1,4-phenylene] (P2, alkyl = butyl, octyl and dodecyl) have been synthesized by Grignard coupling and FeCl3 oxidation methods, respectively. Spectral measurements indicate that they are highly fluorescent, with quantum yields comparable to those of their alkyl(R)-functionalized analogues, poly(3-alkyl-2,5-thiophenediyl-1,4-phenylene-alt-4-alkyl-2,5-thiophenediyl-1,4-phenylene) (P1ʹ, alkyl = butyl, octyl and dodecyl) and poly(4,4ʹ-dialkyl-2,2ʹ-bithiophene-5,5ʹ-diyl-alt-1,4-phenylene) (P2ʹ, alkyl = butyl, octyl and dodecyl). P1 and P2 are thermally less stable than P1ʹ and P2ʹ, because of the alkylthio group instead of an alkyl group. Modulated differential scanning calorimetry (MDSC) studies reveal a plasticizing effect exerted by the long side chains on the glass transitions (Tg) of the polymers. The P2 series of polymers exhibit a much higher Tg than the P1 series, ascribable to a greater resistance to segmental rotation in the former structure. A cyclic voltammetric study of polymers indicates that they are n-dopable. When doped by I2 or FeCl3, high doping levels of the polymers can be deduced from the weight change, XPS and elemental analysis, but conductivities are not high.