The Study of Electronically Conducting Polymers with Highly Reversible p- & n-Doping

Abstract

Poly[3-(3,4,5)-trifluorophenyl]thiophene (PTFPT) and poly[(2,7- fluoren-9-one)-alt-(5,5'-(3,3'-di-n-octyl-2,2'bithiophene))] (PFDO BT-HH, HH=head-to-head) were used to compare the relative stability of their electrochemical p- and n-doping. Both polymers were expected to exhibit an optimized π-electron density in the polymeric backbone of polythiophene either by attaching a pendant (redox-inactive) electron-withdrawing group in the 3-position of the heterocyclic monomer, or by obtaining a co-monomer containing π-conjugated bithiophene and a redox- active subunit. It is shown that PTFPT is sensitive to over- reduction at high cathodic polarizations whereas PFDOBT-HH, in which n-doping occurs in two steps, is much more stable with respect to over-reduction. This is explained by the fact that bithiophene and fluoren-9-one subunits in PFDOBT-HH are conjugated, and hence, the injected negative charge is distributed on both subunits, thus stabilizing the doped polymeric structure.