Electronic properties of the linear ladder polymer, poly[4‐(3‐pyridyl),8‐methyl,2,3–6,7‐quinolino] (PPMQ)

Electronic paramagnetic resonance (EPR) and conductivity of pristine and iodine‐doped PPMQ were studied. The pristine polymer EPR signal exhibited a Lorentzian line shape. Unpaired spin density measurements indicated that the spin concentrations of the undoped polymer lie in the range of one spin per 150–190 repeat units at room temperature. The peak‐to‐peak width doubled, the line shape became asymmetric and the spin concentration in the polymer increased slightly after doping with iodine. EPR saturation experiments show that the spin lattice relaxation time T1 is sensitive to trace impurity. Considerable reduction of T1 after doping with iodine shows strong coupling between the spin system and N‐iodonium nucleus. Conductivity increases up to 5 orders of magnitude by iodine doping; at room temperature, the best value found was 0.017 S/cm. The activation energy for conductance after doping is about half that of pristine polymer.