INTERACTION OF OXYGEN WITH CONJUGATED POLYMERS - CHARGE-TRANSFER COMPLEX-FORMATION WITH POLY(3-ALKYLTHIOPHENES)

Molecular oxygen forms a reversible charge transfer complex (CTC) with poly(3-alkylthiophenes). The complex is weakly bound but possesses a distinct absorption band in the visible region. The electronic propert ies of the neutral polymer are modulated by the CTC. The extent of mod ulation of these properties is proportional to oxygen pressure and is fully reversible. Analysis of poly(3-hexylthiophene) field effect tran sistors under increasing pressures of oxygen shows that the carrier co ncentration increases, conductivity increases, and the charge carrier mobility is lowered by the formation of the charge transfer complex. T he CTC manifests itself as a fluorescence quencher of mobile polaronic excitons, and it explains why oxygen quenches luminescence with much greater efficiency than predicted by a collisional quenching model. Im plications of the charge transfer complex on the photochemistry of pol y(3-alkylthiophenes) and photosensitization of singlet oxygen are disc ussed.