Porphyrins are 18pi-conjugated aromatic macrocycles derived from four pyrroline subunits. Many porphyrins occur in nature, such as in green leaves and red blood cells and this has led to the extensive investigation of their chemistry over the past century.

Subporphyrins, on the other hand, were first developed in 2006 by the group of Atshiro Osuka and they are very much newcomers to the porphyrinoid family. But what are they? Subporphyrins are ring-contracted porphyrins with three pyrrole units and a bowl-shaped 14pi-aromatic circuit. Although the chemistry of subporphyrins is still at the infant stage they already exhibit interesting properties such as 14pi-bowl structures, intense green fluorescence and large substituent effects.

In their Dalton Transactions Perspective, Yasuhide Inokuma and Atsuhiro Osuka, from Kyoto University, Japan, discuss their recent progress in this new area of subporphyrin chemistry and the amazing splitting reactions of expanded porphyrins that lead to new porphyrins and subporphyrins.