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 photodonors and a monoprotonated pentapyrrolic sapphyrin acceptor. These complexes 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 CD 2 Cl 2 (as judged by 1 H NMR spectroscopic means). Upon irradiation at 417 nm, singlet−singlet energy transfer from the porphyrin to the sapphyrin subunit takes place readily with energy transfer dynamics that are consistent with a Förster-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.