UNIQUE OPTICAL AND DOPING BEHAVIOR OF PI-CONJUGATED POLYMERS CONSTITUTED OF ELECTRON-ACCEPTING PYRIDINE AND ELECTRON-DONATING THIOPHENE UNITS

Electrically conducting pi-conjugated heteroaromatic copolymers poly(pyridine-5,2-diyl-thiophene-2,5-diyl) PTpy and its analogues have been synthesized in high yields by dehalogenation polycondensation of the corresponding dihaloaromatic compounds with zerovalent nickel complex. PTpy has Mw of 5400 and [eta] of 2.26 dL g-1. The polymers are soluble in formic acid, and their electronic as well as fluorescence spectra give rise to visible and fluorescence peaks whose positions indicate occurrence of intramolecular charge transfer in the polymer molecules. They show unique cyclic voltammograms with unusually large potential difference between the p-doping (0.4 V vs Ag/Ag+) and p-undoping peaks (-1.7 V), which is accounted for by an EC mechanism. Random copolymers of pyridine-2,5-diyl and thiophene-2,5-diyl show similar unique optical and electrochemical behaviors.