An unconventional nano-AIEgen originating from a natural plant polyphenol for multicolor bioimaging

Biocompatible aggregation-induced emission (AIE) materials from natural resources are of great interest for a variety of potential applications. Here, we report the unconventional AIE nature of the green tea polyphenol epigallocatechin gallate (EGCG), which is investigated by observing the disappearance and reoccurrence of fluorescence when EGCG is dissolved and recrystallized in aqueous solutions. The intermolecular through-space conjugation and structural rigidification induced by multiple intermolecular H-bonds play critical roles in the AIE phenomenon. This inspires the development of a multicolored, monodisperse, photostable, and non-toxic nano-AIE luminogen (nano-AIEgen), which is simply prepared by polyphenol-amine-based crosslinking in aqueous solutions, demonstrating great potential for living cell bioimaging. Our strategy to develop nano-AIEgens using AIE-active hydrophilic natural products—e.g., plant polyphenols, such as tannic acid, that exhibit similar AIE characteristics—can help push the boundary of the exploration of various novel, large-scale, biocompatible, water-soluble, and degradable AIE materials from natural resources. [Display omitted] •AIE phenomenon for EGCG in the solid state•The AIE activity results from through-space conjugation by intermolecular H-bonds•The EGCG nano-AIEgens may be successfully used to image living cells As a plant polyphenol, epigallocatechin gallate is highly soluble in water and non-toxic. Here, Lu et al. demonstrate an interesting AIE phenomenon in common natural products and propose strategies for screening and developing hydrophilic AIEgens from natural products.