An Unconventional Nano-Aiegen Originating from a Natural Plant Polyphenol for Multicolor Bioimaging

The unconventional aggregation-induced emission (AIE) nature of the green tea polyphenol epigallocatechin gallate (EGCG) was first discovered and investigated by observing the disappearance and reoccurrence of fluorescence (FL) when EGCG was dissolved and recrystallized in aqueous solution. The intermolecular through-space conjugation and structural rigidification induced by multiple intermolecular H-bonds play critical roles in the AIE phenomenon. This inspired the development of a multicolored, monodisperse, photostable and nontoxic nano-AIE luminogen (nano-AIEgen), which was simply prepared by polyphenol-amine-based crosslinking in aqueous solution, and has demonstrated great potential for living cell bioimaging. The strategy to develop nano-AIEgens by assembling overlooked AIE-active hydrophilic natural products (e.g., plant polyphenols, such as tannic acid (TA), which has similar AIE characteristics) rather than traditional hydrophobic AIEgens could help expand the exploration boundary of novel, large-scale, biocompatible, water-soluble, and degradable AIE materials from natural resources.