The Design and Synthesis of New NIR-Active Sensitizers for Use in Photochemical Processes and Controlled Polymerizations

Abstract

The NIR-absorbers S1-S3 derived from heptamethines covering the absorption from 700-1100 nm were used to study photopolymerization of vinyl monomers in organic and aqueous surroundings. Polymerization conditions were chosen to follow an ATRP protocol using ethyl α-bromophenylacetate (EBPA) as initiator in organic surroundings and ethyl-2 bromoisobutyrate in aqueous medium. Excitation proceeded at 820 nm using a new high power NIR-LED. PtBr₄, AuBr₃, and NiBr₂ served as metal catalyst to complement previous findings where CuBr₂/L and FeBr₃/Br^- served as metal catalysts in photo-ATRP explorations using NIR-radiation for excitation. UV-Vis-NIR titration experiments were pursued to receive more detailed information about interactions between the sensitizer (Sens) and the 3d-metal ion added. Except for NiBr₂, all metal salts resulted in a change of the absorption spectrum. This occurred bathochromic in case of FeBr₃ addition and hypsochromic upon addition of CuBr₂, PtBr₄, and AuBr₃.