Syntheses and characteristics of porphyrin derivatives bearing fused five-membered rings at the periphery

Recently, porphyrin derivatives having ring-fused structures at the periphery have attracted attention by virtue of their unique optoelectronic characteristics. This manuscript surveys the syntheses and properties of porphyrin derivatives having fused five-membered rings at the periphery. Porphyrin derivatives with fused five-membered rings have been revealed to exhibit unique properties, which are different from those having fused six-membered rings at the periphery. For instance, porphyrins with fused five-membered rings exhibit expanded aromatic and anti-aromatic circuits passing through the outer rim of the fused rings. The expanded aromatic and anti-aromatic circuits severely affect the electronic structures of the porphyrin derivatives.