Noncharged and Charged Monodendronised Perylene Bisimides as Highly Fluorescent Labels and their Bioconjugates

A series of water-soluble, hydroxylated and sulphated, polyglycerol (PG) dendronised, monofunctional perylene bisimides (PBIs) were synthesised in three generations. Their photophysical properties were determined by absorption and emission spectroscopy and their suitability as potential biolabels examined by biological in vitro studies after bioconjugation. It could be shown that the photophysical properties of the PBI labels can be improved by increasing the sterical demand and ionic charge of the attached dendron. Thereby, charged labels show superior suppression of aggregation over charge neutral labels owing to electrostatic repulsion forces on the PG-dendron. The ionic charges also enabled a reduction in dendron generation while retaining the labels' outstanding fluorescence quantum yields (FQYs) up to 100 %. These core-unsubstituted perylene derivatives were successfully applied as fluorescent labels upon bioconjugation to the therapeutic antibody cetuximab. The dye-antibody conjugates showed a strongly enhanced aggregation tendency compared to the corresponding free dyes. Biological evaluation by receptor-binding, cellular uptake, and cytotoxicity studies revealed that labelling did not affect the antibody's function, which renders the noncharged and charged dendronised PBIs suitable candidates as fluorescent labels in biological imaging.