Copper-Free Clickable Coatings

The copper-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) is extensively used for the functionalization of well-defined polymeric materials. However, the necessity for copper, which is inherently toxic, limits the potential applications of these materials in the area of biology and biomedicine. Therefore, the first entirely copper-free procedure for the synthesis of clickable coatings for the immobilization of functional molecules is reported. In the first step, azide-functional coatings are prepared by thermal crosslinking of side-chain azide-functional polymers and dialkyne linkers. In a second step, three copper-free click reactions (i.e., the Staudinger ligation, the dibenzocyclooctyne-based strain-promoted azide-alkyne [3+2] cycloaddition, and the methyl-oxanorbornadiene-based tandem cycloaddition-retro-Diels-Alder (crDA) reaction) are used to functionalize the azide-containing surfaces with fluorescent probes, allowing qualitative comparison with the traditional CuAAC.