Synthesis and optical properties of water-soluble polyglycerol-dendronized rylene bisimide dyes

Four new water-soluble polyglycerol-dendronized perylene, terrylene, and quaterrylene bisimides have been synthesized and characterized with respect to their optical properties in polar organic solvents and water by using UV/Vis and fluorescence spectroscopy. All of these dyes were highly soluble in water, but the size of the chosen polyglycerol dendron was only sufficient to completely suppress dye aggregation for the core-unsubstituted perylene derivative. Their high solubility in water and their absorption and emission wavelengths up to the NIR region make the core-unsubstituted perylene and terrylene bisimides ideal candidates for applications in bioimaging, whilst the lack of fluorescence for quaterrylene bisimide in all polar solvents does not warrant further investigation of this chromophore in fluorescence and imaging applications. Likewise, tuning of the emission of rylene bisimides towards longer wavelengths by employing electron-donating bay substituents is not a promising strategy, owing to the lower fluorescence quantum yields in polar solvents and, in particular, in water.