ELECTROCHEMICALLY POLYMERIZED TERTHIOPHENE DERIVATIVES CARRYING AROMATIC SUBSTITUENTS

A series of terthiophene derivatives substitituted with an aryl group R at the 3'-position of the central thiophene [R = H (1), phenyl (2),4-cyanophenyl (3),4-methoxyphenyl (4),4-pyridyl (5),2-thienyl (6), or 3-methyl-2-thienyl (7)] have been polymerized. Although the substituents force the monomers to a nonplanar conformation, thus preventing the extension of conjugation to the side group, they influence the polymerizability and the properties of the resulting polymers. Solubilities of the oxidation products and inductive effects of the substituents are discussed in order to explain the differences. As-grown films of poly-1,-2,-3,-4, and -6 were soluble in chlorinated organic solvents. Poly-1 consists of monomers and dimers, but the polymerization degree of other soluble polymers was larger, as determined by matrix-assisted laser desorption ionization mass spectroscopy (MALDI-MS). The polymers are mixtures of oligomers in all cases, and the highest observed oligomers were heptamers (with poly-2 and -3). With the exception of poly-1, -4, and -5, the films could be both anodically and cathodically doped. A splitting of the cathodic undoping peak in cyclic voltammograms was observed with poly-6 and -7 and polythiophene. This behavior is analogous to the anodic undoping, suggesting a mechanistic symmetry in the doping processes. Spectral changes during undoping are interpreted by reactions of ionic species having different effective conjugation lengths.