Aromaticity Switching in Porphyrinoids

The aromaticity of porphyrinoids can be substantially altered by reversible modification of their original electronic structures. Well-defined modulators can be used as a means to initiate these modifications, including redox processes, acid-base chemistry, and conformational phenomena. This Focus Review emphasizes the situation for which a single macrocyclic frame alternatively adopts diatropic and paratropic features and both situations are readily and mutually exchangeable. Eventually, such a porphyrinoid transformation can be explored as a suitable element to construct switchable optoelectronic materials.