Synthesis, Optical Properties and Cellular Toxicity of Water-Soluble near Infrared-II Fluorescent Assemblies Based on Pillar[5]arene

The main challenges in second near-infrared region molecular fluorophores are poor water solubility and unknown long-term toxicity at present. Herein, new NIR-II molecular fluorophores have been designed and employed to integrate biocompatible pillar[5]arene with 10 outer triethylene oxide groups for the synthesis of rotaxane IRCR. In addition, PEGylated pillar[5]arenes have been combined for the self-assembly of two supramolecular vesicular systems, i.e., PP5-IR1 and PP5-IR2, affording aqueous solubility and lowered cellular toxicity. In aqueous solution, all these fluorophores displayed room-temperature emission with λ(max) at 986–1013 nm and quantum yields of 0.54–1.45%. They also exhibited good chemical stability and reasonable self-assembled sizes, which may find potential applications in NIR-II imaging. In addition, PP5-IR1 can be used as a fluorescent chemosensor for selective recognition of glutathione through the cleavage of dinitrophenyl ether and release the fluorescent dye.