Covalent heterodyads of synthetic chlorophyll derivatives linked with linear rigid substituents at the 20-positions constructing photoexcited energy transfer systems

Abstract

Chlorophyll and bacteriochlorophyll pigments are important porphyrinoids, which play key roles in light absorption, energy migration/transfer, and electron transfer in natural photosynthesis. Dyads of such pigments have attracted much attention from the viewpoints of mimicking photosynthetic light-harvesting and charge-separating systems. In this study, we report the synthesis and optical properties of heterodyads of zinc chlorin and free-base bacteriochlorin covalently linked by linear rigid substituents at the 20-position, which were prepared from naturally occurring chlorophyll-a. A free-base bacteriochlorin moiety accepted the singlet excitation energy from the zinc chlorin in the heterodyads. In the co-aggregate systems of heterodyads with chlorosomal self-assemblies, the latter transfers the singlet excitation energy to the bacteriochlorin moiety of the former, which are useful for artificial chlorosomal supramolecular light-harvesting systems.