Photophysical Properties of Ag(I) Size-tunable Covalent Porphyrinic Cages and their Encapsulation Complexes

Functional systems based on molecular capsules have shown a great potential as nanoreactors, molecular recognition systems or drug carriers since they provide a confined a three-dimensional environment that enhance molecular reactivity. The components that define these functional systems are not only structural, but active species can be selected to shape the activity within the cavity. One manner of controlling the binding and delivery of a guest molecule is to incorporate constituents of the molecular capsule that can respond to an external stimulus by provoking a conformational change that modifies the host encapsulation properties. Among the possibilities of designing molecular cages, metalated or free-base porphyrins are attractive due to their chemical stability provided by covalent structures and the expected ?-? interactions or coordination bonds with guest molecules. We recently reported on the photophysical properties of four flexible bis-porphyrin covalent cages incorporating either Zn metalated or free-base porphyrins, linked by 1,2,3-triazolyl ligands, and of their Ag(I) complexes.2 Here we report on the process of encapsulation of a guest (ethionamide, an antibiotic), followed by absorption and emission spectroscopy, once the cavity of the cage is enlarged by the addition of Ag(I). The photoinduced processes occurring in the host-guest systems will be discussed.