π-Conjugated Poly(dithiafulvene) by Cycloaddition Polymerization of Aldothioketene with Its Alkynethiol Tautomer. Polymerization, Optical Properties, and Electrochemical Analysis

π-Conjugated polymers ( 2 ) having electron-donating dithiafulvene units in the main chain were prepared by the addition reaction of aldothioketenes derived from π-conjugated diynes (1,4-diethynylbenzene, 4,4‘-diethynylbiphenyl, 2,7-diethynylfluorene, and 1,3-diethynylbenzene) with their alkynethiol tautomers. The structures of the polymers were supported by IR and 1 H NMR spectra and by elemental analyses. The obtained polymers were soluble in DMSO and DMF and partially soluble in acetone and methanol. The absorption peak due to the π−π* transition of 2a (prepared from 1,4-diethynylbenzene) was largely bathochromic shifted in comparison with that of 2-benzylidene-4-phenyl-1,3-dithiole ( 3 ) as a model compound. This red shift is ascribed to an effective expansion of the π-conjugation system in 2a . In the case of 2d (prepared from 1,3-diethynylbenzene), the absorption maximum was same as that of 3 . This result was caused by the fact that the π-conjugation is not expanded through 1,3-disubstituted benzene. The cyclic voltammograms show that an anodic shift and a broadening of the oxidation peak for the dithiafulvene unit for 2a was observed compared with that of 3 . Before doping, 2a exhibits an electrical conductivity of 3 × 10 -7 S cm -1 as measured on a cast film from 1,3-dimethyl-2-imidazolidinone. Oxidation with iodine raised the electrical conductivity to 1 × 10 -3 S cm -1 .