Role of Polymer Structure on the Conductivity of N‐Doped Polymers

The n‐doping of several conjugated co‐polymers based on perylene diimide (PDI) and napthalene diimide (NDI) acceptors co‐polymerized with ethynylene, ethylene, and bithiophene by the dimeric dopant (2‐Cyc‐DMBI) 2 is reported. The n‐doping reactions are confirmed in solution by UV–Vis–NIR spectroscopy and in thin films with photothermal deflection spectroscopy (PDS). The reduced species of the ethynylene‐linked polymers are found to be more delocalized along the polymer backbone than the bithiophene‐linked polymers by comparison of the absorption spectra. A high conductivity of 0.45 S cm −1 is measured for the ethynylene‐linked polymer P(PDI2OD‐A). In contrast, neither of the two bithiophene‐linked polymers, P(NDI2OD‐T2) and P(PDI2OD‐T2), achieve conductivities greater than 4 × 10 −3 S cm −1 . Furthermore, there is no correlation between the conductivity of the doped films and the mobility of the pure films used in this study. Grazing incidence X‐ray diffraction (GIXD) measurements of the films find that a similar doped phase forms irrespective of the crystallinity of the pure host polymer. In absence of a significant difference in morphology, these results suggest a link between the polaron delocalization length of the polymers and the conductivity, and more fundamentally between the backbone structure of the polymer and the polaron delocalization length.