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 substituent s force the monomers to a nonplanar conformation, thus preventing the extension of conjugation to the side group, they influence the polymer izability and the properties of the resulting polymers. Solubilities o f 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 o ther soluble polymers was larger, as determined by matrix-assisted las er desorption ionization mass spectroscopy (MALDI-MS). The polymers ar e mixtures of oligomers in all cases, and the highest observed oligome rs 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 analo gous 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 leng ths.