Aluminum corrolin, a novel chlorophyll analogue.

A corrole-based chlorophyll analogue has been prepared, based on the notation that the major differences between the prosthetic groups of chlorophylls and hemes are the presence of a non-transition metal (Mg vs. Fe) and one reduced double bond in the porphyrin ligand. As corroles act as tri- rather than dianionic ligands, the analogy requires the insertion of aluminum into the macrocycle and the reduction of one of its double bonds, two reactions that have not been previously reported with any corrole. The aluminum complexes of both the corrole and the corrolin (the dihydrocorrole) display fluorescence quantum yield that are much larger than of chlorophyll and of all other previously reported synthetic analogues. The results suggest that the light metal atom ion is responsible for low intersystem crossing probability to the triplet excited state and the structural rigidity of the hexa-coordinated complexes for reducing the probability of internal conversion.