Charge-neutral and self-doped cyclopentadithiophene-based conjugated polymers: Influence of side chain on optical, electrical, and thermoelectric properties

Abstract

Water-soluble cyclopentadithiophene-based conjugated polymers (CP1–Na, CP2–Na, and CP3–Na) having the sodium propanesulfonate side group and with different comonomer units were synthesized by Suzuki-Miyaura polymerization under the microwave heating at 90 °C for 8 h. Number-averaged molecular weights determined by GPC analyses after exchanging the counter cation ranged from 6200 to 10400. TGA measurements revealed that the degradation temperatures at 10% weight loss of polymers exceed 250 °C. UV–vis–NIR spectra exhibited broad absorptions at 950–1000 nm originated from the polaronic band, in which the intensity of this band was largest for CP3–Na with the bis(methylsulfanyl)methylene unit. The spin density calculated from EPR spectra was largest for CP2–Na with triethylene glycol chains (6.4 × 1016 for 1 mg). The electrical conductivity, Seebeck coefficient, and power factor of CP3–Na were estimated as 9.1 × 10−3 S cm−1, 34 μV K−1, and 1.1 × 10−3 μW m−1 K−2, respectively.