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 its hexyl derivative, PEDOTh-C-6(Ni), have been prepared by organometallic dehalogenation polycondensation of 2,5-dichloro-3,4-ethylenedioxythiophene and 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 solutions and in a solid state, led to weakening of the original pi-pi* peaks and rise of new peak(s) in a region of 800-1500 nm. The p-doping of PEDOTh-C-6(Ni) caused not only a decrease in the intensity of H-1 NMR signals of the bridging ethylene hydrogens but also a decrease in that of the hexyl side chain, suggesting a strong interaction of the p-dopant with the side chain. NMR data of poly(3-methoxythiophene-2,5-diyl) also supported an assumption that p-doping brings about a severe change in electronic state of the substituent 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 density of the polymer and its XRD data. (C) 2001 Elsevier Science Ltd. All rights reserved.