Mixed Ionic–Electronic Conduction, a Multifunctional Property in Organic Conductors

Organic mixed ionic–electronic conductors (OMIECs) have gained recent interest and rapid development due to their versatility in diverse applications ranging from sensing, actuation and computation to energy harvesting/storage, and information transfer. Their multifunctional properties arise from their ability to simultaneously participate in redox reactions as well as modulation of ionic and electronic charge density throughout the bulk of the material. Most importantly, the ability to access charge states with deep modulation through a large extent of its density of states and physical volume of the material enables OMIEC‐based devices to display exciting new characteristics and opens up new degrees of freedom in device design. Leveraging the infinite possibilities of the organic synthetic toolbox, this perspective highlights several chemical and structural design approaches to modify OMIECs’ properties important in device applications such as electronic and ionic conductivity, color, modulus, etc. Additionally, the ability for OMIECs to respond to external stimuli and transduce signals to myriad types of outputs has accelerated their development in smart systems. This perspective further illustrates how various stimuli such as electrical, chemical, and optical inputs fundamentally change OMIECs’ properties dynamically and how these changes can be utilized in device applications. Structural and dynamic tuning of organic mixed ionic–electronic conductors influence a myriad of functional properties: energy levels, conductivity, color, modulus, and volume for a diverse range of real‐world applications. Several chemical and structural design approaches to modify OMIECs’ properties are highlighted, and how various stimuli such as electrical, chemical, and optical inputs fundamentally change OMIECs’ properties dynamically, along with how these changes can be utilized in device applications, is discussed.