On/off Switching of the Fluorescence of Porphyrin Supramolecular Aggregates Modulated by pH

Abstract

Aggregation of small molecules on a polymeric matrix, driven by electrostatic interactions, provides a simple and attractive strategy for building well-defined supramolecular species. By choosing matrices of different nature and length together with the proper experimental conditions (pH, ionic strength, etc.) it is possible to tune the extent of aggregation and/or the size of the aggregates and, thereby, the “macroscopic” properties (absorption and emission features, redox potentials, etc.) of the supramolecular complex. It turns out that porphyrins are particularly good “bricks” for building these complexes, given their well known and tunable electronic properties (i.e., through the insertion of different metal ions and/or substituents on the porphyrin ring), . Recently, it has been reported that the water-soluble anionic porphyrin, mesotetrakis 4-sulphonatophenyl)-porphyrin (H₂TPPS) (Figure 1), interacts with the protonated form of polylysine leading to the formation of aggregates [1].