Energy and Electron Transfer in Synthetic Oligoproline-BridgedPorphyrin Donor–Acceptor Molecules

Oligo-l-proline-bridged bis(porphyrin) compounds were synthesized. The protected oligoprolines in ethanol might take a fairly stable helical conformation at an oligomerization number ≥4. An intramolecular singlet energy transfer occurred in ethanol from a photoexcited zinc porphyrin moiety in the N-terminal to a metal-free porphyrin moiety in the C-terminal at the same efficiency as from the zinc porphyrin moiety in the C-terminal to the metal-free porphyrin moiety in the N-terminal. A photoinduced electron transfer also occurred in ethanol from the zinc(II) porphyrin to the iron(III) porphyrin in the molecule, which was independent of the direction of the spacer as well as the energy transfer. A weak change in the intramolecular electron-transfer efficiency with the distance between the zinc and iron porphyrins suggested that electrons should move through the amide bonds in the oligoproline linkage.