Synthesis of chlorophyll-BODIPY conjugates and their intramolecular excitation energy transfer

Abstract

Zinc 3-hydroxymethyl-pyropheophorbides-[Formula: see text] covalently linked with an 8-aryl-1,3,5,7-tetramethyl-BODIPY moiety in the 17-substituent were synthesized by chemically modifying naturally occurring chlorophyll(Chl)-[Formula: see text]. The synthetic Chl–BODIPY conjugates in tetrahydrofuran exhibited sharp visible absorption and weak circular dichroism spectra, indicating that their molecules were fully dispersed in the solution. In their ground states, no intramolecular interaction between the Chl and BODIPY parts was observed. By contrast, singlet excitation energy was efficiently transferred from the photoexcited BODIPY moiety to zinc chlorin moiety within their molecules. The intramolecular energy transfer efficiencies exceeded 90% and were independent of the linkages including ester and amide bonds as well as methylene and hexamethylene spacers.