Effects of pH on the photophysics of conjugated polyelectrolyte complexes

We have previously reported the formation of complexes between oppositely charged, conjugated polyelectrolytes (CPECs), resulting in electronic energy transfer between the donor and acceptor components. The ionic self-assembly process that forms CPECs is heavily influenced by environmental circumstances including solvent composition, temperature, and pH. In this article, we report the effect of polyelectrolyte chain protonation on complex formation and resulting energy transfer. The particular polyelectrolytes used in this study were a pH inactive energy donor and an acceptor polymer with protonatable sidechains. We find that over a large range of acidic pH, the optical properties do not change appreciably up to precipitation (pH 3). Surprisingly in the basic regime where the acceptor polymer is fully deprotonated, complex formation is hindered. However, at pH 11, which corresponds to an excess ion concentration of 0.001 M, the photophysical properties of the complex begin to once again resemble that of the neutral or acidic environments. Our results show that the CPEC displays impressive stability over a relatively broad range of proton concentrations, which may have implications for the construction of supramolecular light-harvesting assemblies. (C) 2017 Elsevier Ltd. All rights reserved.