Polymeric organosilicon systems .26. Synthesis and photochemical and conducting properties of poly[(tetraethyldisilanylene)oligo(2,5-thienylenes)]

A series of poly[(tetraethyldisilanylene)(2,5-thienylenes)(n)] (1-5) with n 1-5 were synthesized. The NiCl2(dppe)-catalyzed Grignard coupling of 1,2-bis(5-bromothien-2-yl)tetraethyldisilane (6) and 1,2-bis(5'-bromo-2,2'-bithien-5-yl)tetrathyldisilane (7) with 1 equiv of Mg afforded polymer 2 (M(w) = 53 000, 75% yield) and 4 (M(w) = 29 500, 97% yield), respectively, while similar reaction of the di-Grignard reagent obtained from 6 and 7 with 1 equiv of 2,5-dibromothiophene afforded the respective polymers 3 (M(w) = 47 000, 77% yield) and 5 (M(w) = 17 000, 78% yield). The sodium condensation of 2,5-bis(chlorodiethylsilyl)thiophene afforded polymer 1 (M(w) = 20 000, 32% yield). Irradiation of polymers 1-5 with a low-pressure mercury lamp resulted in cleavage of the silicon-silicon bonds, but the reactivity decreased with an increase in the number of thienyl units. When the films of polymers 2-5 were doped with FeCl3 vapor, conductivities of doped films were determined to be 10(-5)-10(-3) S cm(-1) (in vacuo).