Porphyrin dendrimers as effective dye bleaching sensitizers in high water content solutions

In this work, a comparative analysis on dye bleaching capacity of porphyrin-core dendrimers (Pf-Ds) of two different sizes (first and second generations) in high water content media is carried out. First, a series of new second-generation compounds were synthesized and characterized by absorption and fluorescence spectroscopies. These dendrimers showed high solubility in hydro-alcoholic solutions, allowing the transport of free-base tetraphenyl-porphyrin in a medium where, without branching, it would not be soluble. In addition, the triplet states were also characterized by transient spectroscopy, obtaining high intersystem crossing quantum yields. The singlet oxygen quantum yields were estimated and comparable to those of typical porphyrins, which demonstrates that sensitizing capacity of the core is not affected by the extent of dendritic branching. In order to compare the performance of these compounds in pollutant treatment, the effect of branching size on the bleaching of phenolphthalein as a model dye was evaluated. All the compounds showed high photodegradation efficiency via singlet oxygen after short irradiation times under visible LEDs. However, as a general trend, it was observed that first-generation compounds were more effective than second-generation ones. Based on quenching experiments, such results were interpreted in terms of the intermolecular interactions occurring between the reactants and the role played by the length of the dendritic arm.