Porphycenes and Related Isomers: Synthetic Aspects

Porphyrins, called the pigments of life, have been studied for decades. However, the first constitutional isomer of porphyrin, porphycene, was not synthesized until 1986. This milestone marked the beginning of a new era in the field of porphyrinoids and presented opportunities for the creation of an abundance of new pigments. The unique structural and electronic features of these compounds give rise to interesting physical and optical properties with applications in biomedicine and materials science. This review focuses on the synthetic methodologies available for the preparation of porphycenes (functionalized porphycenes, extended porphycenes, benzoporphycenes, naphthoporphycenes, and heteroanalogues) and the other known isomers, namely, corrphycene, hemiporphycene, and isoporphycene. Although the classical synthetic approaches are discussed, particular emphasis is placed on improvements to the known methodologies and recent advances in the field.