Picosecond dynamics of energy transfer in porphyrin-sapphyrin noncovalent assemblies

The picosecond dynamics of noncovalent ensembles for energy transfer based on anion chelation are reported. The photoactive noncovalent complexes are assembled via salt-bridge formation between carboxyl-containing porphyrin p hotodonors and a monoprotonated pentapyrrolic sapphyrin acceptor. These com plexes are formed with a K-a of ca. 10(3) M-1 upon mixing the receptor and substrate in their respective free-acid and free-base forms in CD2Cl2 (as j udged by H-1 NMR spectroscopic means). Upon irradiation at 417 nm, singlet- singlet energy transfer from the porphyrin to the sapphyrin subunit takes p lace readily with energy transfer dynamics that are consistent with a Forst er-type mechanism. The title systems thus appear to be prototypic of a new kind of noncovalent energy transfer modeling that is predicated on the use of anion chelation.