Near-Infrared Photoinduced Copper-Catalyzed Azide-Alkyne Click Chemistry with a Cyanine Comprising a Barbiturate Group

A new near-infrared (NIR) photosensitization system for the activation of a copper-catalyzed azide-alkyne cycloaddition click reaction (CuAAC) is reported. Selected cyanines comprising either a cationic or zwitterionic structural pattern were tested for their photosensitization activity to generate Cu(I) by photoreduction of Cu(II) to trigger CuAAC under NIR light at ambient temperature. The photosensitization system described also facilitates chemical modification of UV-sensitive materials by CuAAC. Upon exposure to light of wavelength 790 nm under anaerobic conditions, the cyanine with a zwitterionic structure comprising a barbiturate group; that is 5-(6-(2-(3-ethyl-1,1-dimethyl-1H-benzo[e]indol-2(3H)-ylidene)ethylidene)-2-(2-(3-ethyl-1,1-dimethyl-1H-benzo[e]-indol-3-ium-2-yl)vinyl)cyclohex-1-en-1-yl)-1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydropyrimidin-4-olate in combination with Cu(II)-N,N,N ',N '',N ''-pentamethyldiethylene-triamine complex, exhibited excellent activity with high yields. The possibility to synthesise different macromolecular structures such as telechelic polymers and block copolymers by NIR-sensitized CuAAC is demonstrated. The structural and molecular characteristics of the intermediates and final products were evaluated by spectral and chromatographic analyses. This new photochemical reaction opens up new pathways for the macromolecular synthesis of complex macromolecular structures and applications requiring light as an activation tool.