Polymer brush-supported photoredox catalysis

Visible light organo-photoredox catalysis has demonstrated its enormous potential for enabling challenging chemical reactions while being a cheaper and greener alternative to transition metal-based catalysts. In recent years, organic compounds that show thermally activated delayed fluorescence (TADF) have found increasing use as photocatalysts. Nevertheless, contamination of the final product and disposal of the photocatalyst represent weaknesses in such homogeneous catalytic systems. To circumvent these drawbacks, this project aims to develop photocatalytic systems supported by polymer brush-functionalized silica microparticles, enabling their efficient recovery and recycling through simple centrifugation/separation methods. The photocatalyst design relies on the modification of a cyanoarene-based core, using 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) and an acrylate function yielding 3CzIPN-A, a catalytically active co-monomer that can be incorporated within a polymer chain through control radical polymerization. Activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) provided the free copolymer in solution while surface-initiated ARGET ATRP the core-shell particles with the photocatalyst integrated in the brush-shell. The ability of the copolymer of catalysing photoreactions was demonstrated with high yields (~80%) by testing a decarboxylative radical addition reaction. The polymer showed a good separation from the reaction mixture through precipitation; however it was not possible to reuse it under these conditions. Hence, another photoreaction was tested (a photocyclization) showing, with a yield around 40%, a good recyclability for several cycles. The last part of the project involved the synthesis of core-copolymer shell particles that showed an easy separation at the end of the reaction through simple centrifugation, providing a yield of 30% of the desired product.