Role of complexation strength on the photophysical and transport properties of semiconducting charged polymer complexes

The high polymer loading in complexes of conjugated and insulating
polyelectrolytes offers unique opportunities for fabrication of conductive
thick films and bulk structures. The electrostatic interactions in these
systems provide a handle for controlling their structure and properties.
The impact of the charge- mediated complexation strength on the
photophysical and electronic transport properties in blends
of conjugated polyelectrolytes (CPEs) with oppositely charged
polymeric ionic liquids (PILs) is presented here. Varying the frequency of
charged repeat units from 50% to 100% on an anionic polythiophene-based
CPE and a complimentary cationic PIL results in a model system with
controlled complexation strength. In highly charged complexes, the
intimate mixing between the CPE and the PIL is found to reduce the
structural disorder along the CPE backbone, enhancing its intrachain
conjugation and interchain stacking. In weakly charged complexes
(<90%), these chain planarization effects are absent and microphase
separation occurs. At all charge fractions examined, the electrical
conductivity of a doped complex is higher than that of the unblended
constituent CPE. The highest electrical conductivity near 1 S cm-1 is
found for a charge fraction of 100%. These results demonstrate the
potential for designing effective electrical conductors using
electrostatic complexation.