Impact of Side-Chain Polarity and Symmetry on the Structure and Properties of Acyclic Dioxythiophene Polymers

Conformationally flexible side-chains on conjugated polymers promote solution processability while significantly impacting solution aggregation, solid-state ordering, and polymer-electrolyte interactions. These side-chains can strongly influence the repeat unit symmetry, polarity, steric bulk, and noncovalent interactions that collectively dictate how polymer chains pack and assemble. Acyclic dioxythiophene polymers (PAcDOTs) are highly redox-active thiophene-based organic mixed ionic-electronic conductors (OMIECs) where both the 3- and 4-positions of the thiophene ring are substituted by alkoxy groups. In this study, we explore the solution and solid-state structures of both symmetric (R1 = R2) and asymmetric (R1 ≠ R2) PAcDOTs, where R1 and R2 are both either nonpolar or amphiphilic, and we observe rich process-structure behavior. The combination of regio-symmetric and amphiphilic side-chains results in a chiral, lyotropic phase in chloroform solutions that persists as a metastable state in thin films. Temperature-dependent grazing incidence X-ray scattering and cross-polarized optical microscopy indicate that PAcDOTs with regio-symmetric linear side-chains can crystallize into highly ordered morphologies upon thermal treatment. Finally, we show that side-chain polarity, symmetry, and thermal annealing affect the electrochemical doping and dedoping processes.