Neutral and Anionic Free-base and Copper Corroles: Structural, spectroscopic and computational analysis and hypercorrole features

We report the synthesis, crystal structure, spectroscopic and computational electronic structural characterization of two copper corroles, [Cu(5,15-bis(4-methylcarboxyphenyl)-10-(2-methylcarboxyphenyl)corrole)] (1Cu) and [Cu(5,15-bis(4-nitrophenyl)-10-(2-methylcarboxyphenyl)corrole)] (2Cu), as well as spectroscopic and computational studies on the corrole ligands (H3L1 and H3L2), in their neutral and anionic forms. We have found that the anionic corroles containing the 4-nitrophenyl substituents in positions 5 and 15 of the corrole ring show hypercorrole behaviour, where the Q-bands are considerably more intense and red-shifted compared to the ones in the 4-methylcarboxyphenyl substituted corroles. Electronic structure calculations using wavefunction methods (CASSCF/NEVPT2) reveal that the intense Q-bands, which extend slightly into the NIR region, are charge-transfer bands from the anionic corrole core to the strongly-electron withdrawing 4-nitrophenyl substituents. Our study provides examples of easy-to-prepare anionic corroles, metallated and unmetallated, that show hypercorrole behaviour and NIR absorption, and thus could find use in hyperthermal processes.