Research on the Creation of High-purity <i>π</i>-Conjugated Polymer Thin Films and their Interface Control

π-Conjugated polymers are polymers in which π-conjugation extends throughout the entire molecular chain. They exhibit electrical conductivity and light emission, enabling the realization of a wide range of organic devices. However, these materials often contain metal impurities derived from the catalyst or oxidant used during synthesis, which can inhibit their inherent functionality. We synthesized π-conjugated polymers using iodine as an oxidant, yielding π-conjugated polymer thin films with high purity. In addition, we demonstrated that the thin film morphology and surface/interface properties can be controlled by adding additives, in addition to the monomer, during thin film fabrication, which can be removed later. Then, we found that the thin films of some π-conjugated polymers also exhibited photo- and electrocatalytic activity for water reduction/hydrogen production and oxygen reduction/hydrogen peroxide production, and that interfacial control could tune their catalytic activity. This review describes an overview of the synthesis, interfacial control, and functional development of π-conjugated polymer thin films with high purity.