Triphenylamine (TPA) radical cations and related macrocycles

Triphenylamine (TPA) derivatives and their radical cation counterparts have successfully demonstrated a great potential for applications in a wide range of fields including organic redox catalysis, organic semiconductors, magnetic materials, etc., mainly because of their excellent redox activity. The stability of TPA radical cation has significant effect on the properties of the TPA-based functional materials, especially in relation to their electronic properties. Considering the instability of parent TPA radical cation, many efforts have been devoted to the development of stable TPA radical cations and related materials. Among them, TPA radical cation-based macrocycles have attracted particular attention because their large delocalized structures can stabilize the TPA radicals, thus endow them with outstanding redox behaviors, multiple resonance structures, and wide application in various optoelectronic devices. In this review, we give a brief introduction of organic radicals and the documented stable TPA radicals. Subsequently, a number of TPA radical cation-based macrocycles are comprehensively surveyed. It is expected that this minireview will not only summarize the recent development of TPA radical cations and their macrocycles, but also shed new light on the prospect of the design of more sophisticated radical cation-based architectures and related materials.