Recent advances in open-shell mixed conductors—From molecular radicals to polymers

Mixed conductors have recently garnered attention in the chemical physicist community due to their distinctive conducting nature and numerous potential applications. These species transport charges via both ionic and electronic pathways, where the coupling between these pathways facilitates an alternative mode of charge transport. Among the various mixed conductors examined, stable open-shell organic compounds are emerging as a promising class of materials. They have the potential to supplant existing organic mixed conductors thanks to their superior conductivity, ease of processing, environmental stability, and functional adaptability. Notably, recent advancements in open-shell macromolecules have been remarkable, ranging from their unprecedented solid-state electrical conductivity to their versatile roles in electrochemistry. Similarly, recent strides in small molecular open-shell species deserve attention. The solid-state electronic properties of these small molecular radicals can be compared to those of macromolecular (non-)conjugated organics materials, and they also play a significant role in wet (electrolyte-based) chemistry. In this review article, we offer a comprehensive overview of open-shell organic compounds, encompassing both small and macromolecular radicals. We particularly emphasize their role as a mixed conductor in various applications, the unique context of each species, and the interconnections between them.