New π-conjugated polymers constituted of dialkoxybenzodithiophene units: synthesis and electronic properties

New stable and conductive polymers constituted of a new fused thiophene unit, 4,8-dialkoxybenzodithiophene, and related copolymers with thiophene were prepared by organometallic polycondensation in high yields. They showed electrical conductivity of 10−2–5 S cm−1 on doping with iodine. Homopolymers were prepared by Ni-promoted dehalogenation polycondensation, and their molecular structures were confirmed by data from IR spectroscopy and elemental analysis. They were partly soluble in organic solvents, and the soluble part gave number average molecular weights, Mn, of 3000–3600 with Mw/Mn value (Mw=weight average molecular weight) of 1.1–2.4 in the GPC analysis; the Mn value corresponds to a degree of polymerization of about eight. Alternative copolymers consisting of the 4,8-dimethoxybenzodithiophene and thiophene or bithiophene units were synthesized by a Pd catalyzed polycondensation. e organic model compounds for the homopolymer and copolymers were synthesized via analogous organometallic coupling reaction, and optical and electrochemical properties of the model compounds were compared with those of the polymers. UV–VIS spectrum of the oligomeric model compounds showed a large bathochromic shift by >50 nm from the monomeric compound. The p-doping of the polymers was reversible, and the iodine-doped polymers were neutralized by hydrazine. Packing structures of the polymers are discussed based on their XRD patterns and density.