Fluorescent water-soluble probes based on dendritic PEG substituted perylene bisimides: synthesis, photophysical properties, and live cell images

Water-soluble dyes based on dendritic polyethylene glycol (PEG)-substituted perylene bisimides were designed and synthesised. According to the distribution of hydrophilic dendritic PEGs, these dyes can be divided into two classes: (I) head-tail structured dyes, in which the hydrophobic perylene bisimides are the heads of the dyes and the hydrophilic dendritic PEG are used as the tails; (II) core-shell structured dyes, in which the hydrophobic perylene bisimides are encapsulated by the hydrophilic dendritic PEG. The aggregation behaviour and optical properties of these dyes were investigated. The two classes of water-soluble perylene bisimides show similar aggregation behaviour, optical and cytocompatibility properties. With increased dendron PEG generation, the aggregation of the PBI in an aqueous solution is completely suppressed by the hydrophilic bulky dendritic PEG groups, and the fluorescence quantum yield increases from 4% to 93%. These dendritic PEG-substituted perylene bisimides have good cytocompatibility. The head-tail structured dyes show a limited cellular uptake process. By contrast, the core-shell structured dyes are efficiently internalised by cells and accumulated in the cytoplasm.