Cation-π Interactions Promoting the Photodynamic Property and Antibacterial Activity

Cation-π interactions between a positively charged cation and an electron-rich aromatic ring have become one versatile strategy to construct advanced engineering materials. Herein, we prepare water-soluble imidazole-based polymers involving cation-π interactions between imidazole and imidazolium moieties, which remarkably enhanced the fluorescence efficiency, photodynamic behavior, and intrinsic antibacterial activity. The presence of cation-π interactions was clearly demonstrated by a red shift in the absorption band and peak-splitting phenomenon in the ¹H NMR results. The copolymer with a molar ratio of 1:1 in imidazole and imidazolium moieties exhibited the highest fluorescence quantum yield in aqueous solution and optimal reactive oxygen species generation capacity that was not observed for the homopolymers. Moreover, the copolymers exhibited superior antibacterial activity against Staphylococcus aureus, owing to the membrane binding affinity via electrostatic force and cation-π interactions among polymers, which caused a disorder in the bilayer and membrane permeabilization. Thus, we provide deep insights into understanding the relationship between the cation-π interaction and properties, which sheds light on developing new photofunctional materials.