Self-aggregation of synthetic zinc 21-hydroxy-121/131-oxo-porphyrins

Zinc complexes of 21-hydroxy-121/131-oxo-porphyrins were prepared by modifying octaethylporphyrin as models of self-aggregative chlorophylls found in extramembranous antennas of green photosynthetic bacteria. Their visible absorption spectra showed that less hindered interactive groups, such as CH2OH and CHO in a synthetic zinc porphyrin molecule were necessary for their self-aggregation in non-polar organic solvents. Zinc 2-hydroxymethyl-12-formyl-porphyrin self-aggregated to form larger oligomers with red-shifted broad visible bands than the 2,13-regioisomer, indicating that the linear location of OH, Zn and CO in a molecule is requisite for similar self-aggregation with natural systems.