Synthesis and properties of π-conjugated poly(dithiafulvene)s by cycloaddition polymerization of heteroaromatic bisthioketenes

pi-Conjugated polymers (2) having electron-donating ditkiafulvene units and typical heteroaromatic (thiophene or pyridine) units in the main chain were prepared by the cycloaddition polymerization of aldothioketenes derived from heteroaromatic diynes (2,5-diethynylthiophene, 2,5-diethynyl-3-hexylthiophene, and 2,5 -diethynylpyridine) with their alkynethiol tautomers. The obtained polymers were soluble in DMSO and DMF. The structures of the polymers were confirmed by H-1 NMR and IR spectra. The UV-vis absorption spectra of 2 suggested that the pi-conjugation systems in the polymers expanded more effectively than the polymer obtained from 1,4-diethynylbenzene reported previously. The cyclic voltammetry analysis of 2a (prepared from 2,5-diethynylthiophene) showed an anodic shift and a broadening of the oxidation peak for the dithiafulvene unit compared with that of 2,6-bis(2-thienyl)-1,4-dithiafulvene (3), due to the effective expansion of the pi-conjugation in 2a. All polymers 2 formed soluble charge-transfer complexes with TCNQ in DMSO. The UV-vis absorption and IR spectra of the resulting CT complexes indicated that two different types of TCNQ, anion radical of TCNQ and partially charge transferred TCNQ, interacted with the ditkiafulvene unit in 2. Undoped polymer 2c (prepared from 2,5-diethynylpyridine) showed an unusual high electrical conductivity of 1.6 x 10(-4) S/cm due to incorporation of the pi-deficient pyridine unit in the dithiafulvene polymer. The CT complex of 2a with TCNQ has a conductivity of 1.0 x 10(-4) S/cm, 2 orders of magnitude greater than that of the uncomplexed polymer 2a.