FLUORESCENCE STUDIES ON A SUPRAMOLECULAR PORPHYRIN BEARING ANTHRACENEDONOR MOIETIES

A tetraphenylporphyrin bearing four anthracene donor moieties -tetra(3 -(9-methyloxyanthracenyl)phenyl)porphyrin, I) was synthesized and full y characterized. Spectroscopic and electrochemical data and results of metallation and intermolecular fluorescence quenching experiments sug gest that there is no appreciable interaction between the porphyrin an d anthracene moieties in I. Although intermolecular quenching of anthr acene fluorescence by 5,10,15,20-(tetraphenyl)porphyrin is not obvious , the fluorescence of the anthracene donors in I is quenched by more t han 90%. On the basis of the fluorescence excitation spectral data, th e quenching observed is attributed to intramolecular singlet-singlet e nergy transfer from anthracene to the porphyrin. However, neither Fors ter's dipole-dipole formalism nor Dexter's electron exchange mechanism can explain adequately this intramolecular energy transfer. Thermodyn amic considerations and solvent-dependent fluorescence data indicate t hat photoinduced electron transfer from singlet anthracene to the porp hyrin can compete with energy transfer in this supramolecular system.