Controlling the aggregation of 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin by the use of polycations derived from polyketones bearing charged aromatic groups

The interaction between 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin and different polycations is studied by UV–vis spectroscopy. Two polycations containing charged aromatic residues (imidazolium and pyridinium) have been easily synthesized by Paal–Knorr reaction of alternating aliphatic polyketones with histamine and 4-picolylamine. It was found that these polymers stabilize the tetra-anionic form of the porphyrin at acidic conditions, and avoid the formation of H- and J-type self-aggregates. Other polycations such as poly(allylamine) and poly(decylviologen) enhance porphyrin self-aggregation. As the latter polymer has also aromatic charged groups, the influence of the polymer structure as a whole in the behavior of the porphyrin/polycation system is highlighted. In this context, similar but not equal results have been found comparing the influence of the polyketone derivative containing pyridinium groups and the polycation poly(4-vinylpyridine) on the porphyrin self-aggregation and acid–base behavior.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Polycations bearing pyridinium, imidazolium, and viologen units influence the aggregation of the tetrakis-(4-sulfonatophenyl)porphyrin. ► The cations also produce changes on the acid–base and luminescent properties of the porphyrin. ► The aggregation state of the porphyrin has been described in the presence of every polycation and as a function of pH. ► The aggregation interactions are based on hydrophobic, aromatic–aromatic, and electrostatic interactions. ► Competition reactions have been evaluated to highlight the strength of the interactions.