Precise Control of Doping Level and Molecular Structure in Conjugated Organic Materials: Property Design Toward Functional Devices

Over the past 30 years, I have pursued research on the precise control of doping levels (DLs) and molecular structure in conjugated organic materials for understanding their molecular properties and applying them to photo- and electroactive materials. In this personal account, an overview of studies analyzing the molecular characteristics of conjugated oligomers-including their optical, electrochemical, thermal, and electrical properties-is provided in relation to the main-chain π-conjugated length, the electron-donating and -accepting nature of side chains, and the DLs. Furthermore, the development of dye molecules and polymeric materials based on these oligomers and their applications in energy-related devices, such as electrochromic smart windows, dye-sensitized solar cells, organic photovoltaics, and organic thermoelectrics, are described. By integrating molecular design with doping control, these efforts bridge the gap between property design and device-level functionality, offering valuable guidelines for the future development of high-performance organic materials.