Transport, magnetic, and optical properties of electrochemically doped poly(1,4-dimethoxy phenylene vinylene)

A coordinated study on electrochemical, magnetic, optical, and transport properties of poly(1,4-dimethoxy phenylene vinylene) (PDMPV) using in situ electrochemical doping techniques is presented. Properties are correlated through a common axis of applied voltage. Electrochemical doping shows ≊100% Coulombic efficiency up to an applied potential of 3.8 V versus lithium in propylene carbonate electrolyte. Conductivity increases in a reversible manner to a maximum of 250 ${\Omega }^{\mathrm{-}1}$ ${\mathrm{cm}}^{\mathrm{-}1}$ and an applied potential of 3.9 V. Potentials in excess of 3.9 V cause an irreversible decrease in conductivity. Spin and charge show a 1:1 relation only to very low doping levels. Two paramagnetic species are produced on doping. A maximum spin concentration is observed at ≊3.7 V. The ultraviolet–visible–near-infrared spectra of doped PDMPV show at least five absorption bands, at 4.8, 3.7, 2.5, 1.7, and 0.6 eV. The first three bands decrease with doping and the latter two increase. When analyzed by the polaron or bipolaron model, the optical data imply significant symmetry breaking. Contributions to the optical activity from polarons and bipolarons are determined from the EPR results and are found to be different for both peaks, implying greater symmetry-breaking effects for polarons. An electrochemical analysis of EPR results suggests that polaron interaction energies are ≊0.45 eV greater than those for bipolarons.