Complexation of a Conjugated Polyelectrolyte and Impact on Optoelectronic Properties

Electrostatic assembly of conjugated polyelectrolytes (CPEs), which combine a π-conjugated polymer backbone with pendant ionic groups, offer an opportunity for overcoming the limited solubility of most semiconducting polymers to make concentrated inks with tunable materials properties and device performance. Complex coacervation, a liquid–liquid phase separation upon complexation of oppositely charged polyelectrolytes in solution, is used to form dense suspensions of π-conjugated material. A model system was used to investigate this complexation behavior of conjugated polyelectrolytes in terms of electrostatic strength, solvent quality, and polymer concentration. The balance of electrostatic interaction between the oppositely charged polyelectrolytes together with their charge compensating counter-ions and solvent quality for the hydrophobic π-conjugated backbone leads to a rich phase diagram of soluble complexes, precipitates, and complex coacervates. The CPE in the polyelectrolyte complexes has an increased π-conjugation length and enhanced emissivity, with ideal chain configurations due to the reduction of kink sites and torsional disorder.