Synthesis of a Novel Family of Electrochemically-Doped Vinyl Polymers Containing Pendant Oligothiophenes and Their Electrical and Electrochromic Properties

Novel electrochemically-doped vinyl polymers containing 2,2‘:5‘,2‘‘:5‘‘,2‘‘‘-quaterthiophene, 4‘,3‘‘‘-dioctyl-2,2‘:5‘,2‘‘:5‘‘,2‘‘‘:5‘‘‘,2‘‘‘‘-quinquethiophene, and 4‘,3‘‘‘‘-dioctyl-2,2‘:5‘,2‘‘:5‘‘,2‘‘‘:5‘‘‘,2‘‘‘‘:5‘‘‘‘,2‘‘‘‘‘-sexithiophene as pendant groups were prepared by anodic polymerizations of the corresponding new vinyl monomers in the presence of tetra- n -butylammonium perchlorate as a supporting electrolyte, and their electrical and electrochromic properties were investigated. The electrochemically-doped polymers, which were obtained as deeply-colored, lustrous films on the surface of the working electrode, were identified as radical-cation salts of pendant oligothiophenes with ClO 4 - as a dopant, having a partially-cross-linked structure due to the coupling reaction of the radical cation of the pendant oligothiophene moiety. The electrical conductivity of these electrochemically-doped polymers increased with increasing conjugation length of the pendant oligothiophenes; the polymer containing the pendant sexithiophene group exhibited a room-temperature conductivity of ca. 10 -4 S cm -1 with an activation energy of 0.25 eV. These polymers undergo a reversible clear color change from green to yellow and vice versa on electrochemical dedoping and doping, constituting a novel class of potential electrochromic materials.