Recent Development of π-Expanded Porphyrin Derivatives by Peripheral Ring Fusion

In recent years, functional molecules involving expanded π-conjugation circuits have attracted attention owing to their merits to construct optoelectronic materials such as photovoltaic cells. Among functional molecules bearing expanded π-conjugation circuits, porphyrin derivatives having ring-fused structures at the periphery have attracted attention as reflected on the fact that a lot of the new derivatives have been synthesized in this decade to develop their unique optoelectronic characteristics. For instance, ring-fused porphyrins exhibit near IR absorption bands due to small HOMO-LUMO gaps derived from the expanded π-conjugation. This manuscript briefly surveys the syntheses and properties of the ring-fused porphyrin derivatives reported since 2010.