The corrole is an aromatic macrocycle in the same family as the porphyrin. Both molecules are formed by four pyrrole rings, but the corrole (Figure ) consists of three rings connected through methylene groups with the remaining connection is through a direct carbon-carbon bond. Due to the conjugated π-system in both molecules, they present with interesting electronic structure and, therefore, have been studied with density functional theory (DFT) and multireference methods even when no metal is coordinated to the ligand. Figure : The molecular structure of the two copper corroles studied. The unfunctionalized copper corrole (left) and the 5,10,15-triphenyl substituted copper corrole (right). Copper in green, nitrogen in blue, carbon in grey, and hydrogen in white.