Synthesis of Fluorescent, Dumbbell-Shaped Polyurethane Homo- and Heterodendrimers and Their Photophysical Properties

Fluorescent dendrimers have wide applications in biomedical and materials science. Here, we report the synthesis of fluorescent polyurethane homodendrimers and Janus dendrimers, which often pose challenges due to the inherent reactivity of isocyanates. Polyurethane dendrons (G1-G3) were synthesized via a convergent method using a one-pot multicomponent Curtius reaction as a crucial step to establish urethane linkages. The alkyne periphery of the G1-G3 dendrons was modified by a copper catalyzed azide-alkyne click reaction (CuAAC) to form fluorescent dendrons. In the reaction of the surfaces functionalized two different dendrons with a difunctional core, a mixture of three dendrimers consisting of two homodendrimers and a Janus dendrimer were obtained. The Janus dendrimer accounted for a higher proportion in the products' distribution, being as high as 93% for G3. The photophysical properties of Janus dendrimers showed the fluorescence resonance energy transfer (FRET) from one to the other fluorophore of the dendrimer. The FRET observation accompanied by a large Stokes shift make these dendrimers potential candidates for the detection and tracking of interactions between the biomolecules, as well as potential candidates for fluorescence imaging.

Automated summary

In this study, fluorescent polyurethane homodendrimers and Janus dendrimers were synthesized overcoming the challenges posed by the reactivity of isocyanates. By using a one-pot multicomponent Curtius reaction, polyurethane dendrons (G1-G3) were successfully synthesized. The alkyne periphery of the dendrons was modified using a copper catalyzed azide-alkyne click reaction (CuAAC) to form fluorescent dendrons. The mixture of two different functionalized dendrons with a difunctional core resulted in the formation of three dendrimers, including two homodendrimers and a Janus dendrimer, with the Janus dendrimer being the predominant product.