Journal of the American Chemical Society, Vol.121, No.10, 2281-2289, 1999
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 CD2Cl2 (as judged by H-1 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 Forster-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.