Neutral poly (3,4-ethylenedioxythiophene-2,5-diyl)s: preparation by organometallic polycondensation and their unique p-doping behavior

Neutral and non-doped poly (3,4-ethylenedioxythiophene), PEDOTh(Ni), and it s hexyl derivative, PEDOTh-C-6(Ni), have been prepared by organometallic de halogenation polycondensation of 2,5-dichloro-3,4-ethylenedioxythiophene an d its hexyl derivative with a zerovalent nickel complex. PEDOTh-C-6(Ni) was soluble in organic solvents and H-1 NMR data indicated that it had an M-n of 11,000. MALDI-TOF mass analysis of PEDOTh(Ni) gave M-n and M-w of about 1700 and 2400, respectively. PEDOTh-C-6(Ni) showed a UV-Vis absorption peak at 546 mn in CHCl3. Electrochemical oxidation of PEDOTh-C-6(Ni) started at about -0.40 V vs Ag+/Ag and gave a peak at 0.20 V vs Ag+/Ag. Chemical and electrochemical oxidation (or p-doping) of PEDOTh-C-6(Ni), both in solution s and in a solid state, led to weakening of the original pi-pi* peaks and r ise of new peak(s) in a region of 800-1500 nm. The p-doping of PEDOTh-C-6(N i) caused not only a decrease in the intensity of H-1 NMR signals of the br idging ethylene hydrogens but also a decrease in that of the hexyl side cha in, suggesting a strong interaction of the p-dopant with the side chain. NM R data of poly(3-methoxythiophene-2,5-diyl) also supported an assumption th at p-doping brings about a severe change in electronic state of the substit uent attached to the polythiophene main chain. PEDOTh(Ni) had a density of 1.71 the molecular packing mode of PEDOTh(Ni) is discussed based on the den sity of the polymer and its XRD data. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.