Highly fluorescent, water-soluble tetrapodal perylene diimides insulated by cationic pendants for live-cell imaging

Perylene diimides (PDIs), particularly the parent core-unsubstituted PDI chromophores, exhibit a pronounced tendency to aggregate in water, resulting in significant fluorescence quenching. Herein we present a new class of highly fluorescent, water-soluble tetrapodal PDI dyes PDI-4Py-n, with the chromophore core surrounded by four pyridinium pendants, which have been fully characterized by several techniques including X-ray crystallography. Due to the spatial isolation and charge repulsion from four cationic pendants, PDI-4Py-n can effectively suppress the chromophore aggregation in relatively concentrated aqueous solutions, thereby preserving the characteristic PDI fluorescence with high photoluminescence quantum yield. Owing to the outstanding fluorescence properties and good biocompatibility, one of PDI-4Py-n has been successfully employed as a lysosome-targetable fluorescent probe for live-cell imaging. This work presents a straightforward synthetic strategy to water-soluble non-aggregating organic dyes and highlights their potential for biomedical applications.