Efficient Intra-Supramolecular Electron Transfer in Zinc Porphyrin-Coumarin Dyads

We report herein the electron transfer process of a novel supramolecular dyads composed of zinc tetraphenylporphyrin (ZnTPP) and zinc 5,15-dinonyl-10,20-diphenylporphyrin (ZnDPP), as electron donors, and ethyl(4-pyridyl) coumarin-3- carboxylate (EPCC), as an electron acceptor, through metalligand coordination bond in dichloromethane. The optical absorption studies revealed the formation of the moderate stable supramolecular donor-acceptor dyads. The fluorescence measurements showed a significant fluorescence quenching of the singlet-excited state of the singlet-excited states of ZnTPP and ZnDPP upon addition of different amounts of EPCC. Such quenching behavior could be attributed to the electron transfer from the singlet-excited state of porphyrin to EPCC. The bimolecular quenching rates were determined to be 1.98×1012 and 7.59×1012 Lmol for ZnTPP-EPCC and ZnDPP-EPCC, respectively, respectively. The fluorescence lifetime measurements suggest fast and efficient intra-supramolecular electron transfer from the singlet states of porphyrin derivatives to EPCC. Furthermore, the formation of the supramolecular dyads was confirmed by the Raman technique and computational studies. The finding that the examined zinc porphyrin - coumarin supramolecular dyads absorb light in a wide range of UV-visible spectrum, fast and efficient electron transfer render the examined supramolecular dyad as simple models for the reaction centers of the artificial photosynthetic systems.