Photophysics of silver(I)-assembled porphyrin cages

We report on the synthesis and solution studies of porphyrin cages assembled with 3-pyridyl appended porphyrins and silver(I) ions. The cages [Ag4(2H-TPyP)2]4+ and [Ag4(Zn-TPyP)2]4+ could be obtained quantitatively, both in concentrated and in diluted solutions, with the addition of 2 equivalents of Ag(I) salt to the porphyrin solution. At variance with other porphyrin assemblies, in [Ag4(Zn-TPyP)2]4+ the central Zn atom is free and available for coordination of guest molecules, making these cages promising candidates as nanoreactors. The process of cage formation in solution has been characterized by means of UV-visible and fluorescence spectroscopy. The photophysics of the cages is governed by weak inter-porphyrin exciton coupling and the measured triplet excited state lifetimes of the assemblies are unusually long. The experimental outcomes lead to exclude a photoinduced electron transfer from the porphyrin to the Ag+ ion within the cages; this result is discussed on the basis of thermodynamic evaluations .