Transparent highly-oxidized conjugated polymer films from solution

The redox states of poly(3-octylthiophene) (P3OT) in solution are studied to address the role of polarons and bipolarons in conducting polymers. By solution doping, oxidation levels up to similar to 0.60 charges per thiophene ring can be attained, much higher than reported previously for pi-conjugated polymers. The results suggest that multiple polarons are present on a single polymer chain at doping levels up to similar to 0.20. Bipolarons are only formed at high doping levels when the charges can no longer be accommodated in individual lattice distortions. At these high doping levels the UV/Vis/nearIR spectra exhibit a single strong electronic absorption in the nearIR region but almost no absorption in the visible regime. Highly transparent, almost colorless, conducting films, can be cast from these doped P3OT solutions. Subsequent reduction of solution-cast highly-doped P3OT is found to result in the neutral films with enhanced intrachain order.