Photophysical and Viscoelastic Properties of Ionically Complexed Conjugated Polyelectrolyte for Printed Soft Electronics

Conjugated polyelectrolytes (CPEs) exhibit a strong interplay between ionic and electronic properties, enabling tunable photophysical properties and charge transport dynamics. Polyelectrolyte complexation represents a versatile self-assembly strategy to control the properties of CPEs by forming dense phases with varying optoelectronic and mechanical characteristics. This study focuses on ionically assembled complexes comprising oppositely charged self-doped CPE (CPE-K) and bottlebrush polyelectrolyte (BPE). It is demonstrated that subtle adjustments in the composition of CPE-K:BPE blends enables tuning of photophysical and viscoelastic properties. It is observed that increasing the CPE-K:BPE monomeric ratio from 1:1 to 1:3 in the initial solution for complexation induces a significant bathochromic shift in the maximum photoluminescence intensity of the dense phase, from 1.8 to 1.4 eV. Additionally, a higher BPE content enhances the softness and adhesion of the solid complex, while maintaining yield-stress behavior and cyclability of the dense phase. The ability to electrochemically and statically dope the CPE-K–BPE complex, effectively modulating its charge transport and optoelectronic properties is also demonstrated. This work underscores the potential of these complex-fluid phases for developing soft, adhesive, and elastic mixed ionic-electronic conductors with tunable properties for functional applications and 3D-printing.