Supramolecular Porphyrin Assemblies for Photosynthetic Antenna Mimics

Abstract

In order to construct artificial functional mimics of photosynthetic antenna complexes, two N-methylimidazole substituents were introduced at the facing meso positions of porphyrin and metalated by Mg²⁺ ion. In contrast to the specific dimer formation of pentacoordinating Zn atom, Mg metal center accepted the 6th ligation by imidazole and extended the slipped cofacial coordination to higher organized structures. FT Ion spray mass spectrum detected porphyrin oligomers up to a pentamer when the sample was prepared from a MeOH solution, and a heptamer from a CHCl₃-MeOH (1/1) solution. When imidazole instead of N-methylimidazole was employed as the porphyrin substituent, Zn²⁺dimer, they further connected each other by hydrogen bonds to extend the supramolecular structure with a characteristic splitting and significant broadening of the Soret band.

Key Words:

• antenna complex
• photosynthesis
• imidazole
• coordination
• H-bonding