Cyclic Triad of Chlorophyll-a Derivative and Its Folded Conformer

A covalently linked triad of zinc pyropheophorbide-a, a derivative of naturally occurring chlorophyll-a as a photosynthetically active pigment, was prepared by full amidation of 1,4,7-triazacyclononane. The synthetic cyclic trimer produced a folded conformer with triple coordination of the amide carbonyl groups to the central zinc atoms from the β-side in a solution, showing large circular dichroism couplets at the Qy and Soret regions that were based on intramolecular exciton coupling of the zinc chlorin components.