DOPED POLYMERS BY OXIDATIVE POLYMERIZATION .4. OXIDATIVE COUPLING OF METHYLATED OLIGOTHIOPHENES BY FECL3-CENTER-DOT-6H(2)O AS A MODEL REACTION FOR THE OXIDATIVE POLYMERIZATION OF THIOPHENE DERIVATIVES

Methylated bi- and terthiophenes (monomers, 1, 3, 5, 8) with one free alpha-position can be oxidized with FeCl3 . 6H(2)0. An irreversible di merization reaction forms dimers of the expected structure. The radica l cations of the monomers also react with free beta-positions of the f ormed dimers (6, 9) having two methylated alpha-positions. The product s of these reactions show alpha,beta' linkages (7, 10, 11). Different beta-positions in end-capped dimers show a graduated reactivity agains t radical cations of the monomers; the free beta-position with the hig her electron spin density can be attacked preferably by an alpha-posit ion of a radical cation of a monomer molecule. No products with beta,b eta' linkages were found. Electrochemical investigations using fast-sc an voltammetry show the formation of alpha,alpha,' linkages of methyla ted oligothiophenes. For bithiophene derivatives, rate constants of th e dimerization process in the range of 10(9) L . mol(-1). s(-1) were d etermined. In comparison with a terthiophene derivative, it was found that the dimerization rates decrease with increasing chain length of t he oligomers.