Polymerization and characterization of 4,4′-bis(alkylsulfanyl)-2,2′-bithiophenes

Regioregular polymers poly[4,4'-bis(butylsulfanyl)-2,2'-bithiophene] (P1) and poly[4,4'-bis(octylsulfanyl)-2,2'-bithiophene] (P2) were prepared from 4,4 '-bis(butylsulfanyl)- and 4,4'-bis(octylsulfanyl)-2,2'-bithiophene, by oxidative polymerization with FeCl3, and characterized by H-1 and C-13 NMR, FT-IR, and UV-vis spectroscopies, atomic force microscopy (AFM), electrical conductivity, and cyclic voltammetry measurements. They exhibit weight-average molecular weights of 8 and 70 kDa, respectively, and are both readily soluble in CHCl3, CH2Cl2, CS2, toluene, and THF. P1 has a lamellar structure, and P2 is a flexible and compact film that can be easily processed and manipulated. In the neutral state, they show UV-vis absorption maxima at about 470 nm in CHCl3 solution and exhibit marked solvatachromism and thermochromism. Furthermore, they can be cast from orange-red solution to form a violet film. The p-doping potentials have been determined, and the possibility of electrogenerating corresponding polymers has been checked. First comparative characterizations of the electrogenerated polymers have been carried out.