Synthesis of Regioisomeric Bacteriochlorophyll-dAnalogues Possessing a Hydroxy Group at the 21- or 31-Position: Their Chlorosome-Like Self-Aggregation in Solid Films

Abstract

Zinc 2(1)- and 3(1)-hydroxy-13-carbonylhexaethylporphyrins 2 and 3 were synthesized by modifying easily available octaethylporphyrin, and the HPLC-separated regioisomers were fully characterized. The latter compound 3(1)-OH-13-C=O-3, which structurally resembled naturally self-aggregative bacteriochlorophyll-d (3(1)-OH/13-C=O), was preferable to make ordered J-aggregates in the solid film, compared to its regioisomeric 2(1)-OH-13-C=O-2. In contrast, more ordered oligomers were obtained by self-aggregation of zinc porphyrin 1 possessing the interactive moieties (3(1)-OH, Zn, 13-C=O) at the same positions, which was prepared by modifying natural chlorophyll-a molecule. The difference between self-aggregation of 1 and 3 was ascribable to the methyl and ethyl groups attached at the 2-position neighboring the 3(1)-OH group which is requisite for self-aggregation; the steric environment around the interactive OH group is important to make highly ordered supramolecules through strong molecular packings.