Self-aggregation of synthetic multi-hydroxylated zinc chlorophylls

A series of zinc 3-hydroxymethyl-131-oxo-(bacterio)chlorins possessing additional hydroxy group(s) on the B-ring were synthesized as models of bacteriochlorophylls-c/d/e, self-aggregative light-harvesting pigments of green photosynthetic bacteria. Tertiary and secondary alcoholic moieties on the 7- and/or 8-position(s) did not significantly interact with any other functional groups in their well-ordered self-aggregates. In contrast, the less sterically hindered primary alcoholic hydroxy group at the 7- and 8-substituents slightly caused random orientations of their molecular transition dipole moments in the supramolecule by unfavorable hydrogen bonding, which was competitive with the original 31-OH.