Many molecules bearing a phenazine core have shown redox activities, either in vivo or in the area of synthetic materials. The computationally directed discovery inspired our focus on N,N-diaryl dihydrophenazines as a potential class of photoredox catalysts (PCs). Through modifying the aryl substituents on both the nitrogen atoms, a library of N,N-diaryl dihydrophenazines possessing strongly reducing ability in their excited states was established. These PCs has been applied to the photoredox organocatalyzed atom transfer radical polymerization of methacrylates and coupling reactions of two small molecules. Further experimental studies and density functional theory calculations disclosed a unique photoexcited intramolecular charge transfer character. We intend to expand the application of N,N-diaryl dihydrophenazines as PCs in radical ring-opening polymerization (RROP) of cyclic monomers, such as functionalized vinylcyclopropanes (VCPs). VCPs generally polymerize through two mechanistic pathways in RROP, affording polymers with mixed linear and cyclobutane units (Figure 1). Historically, the free radical polymerization of VCPs is performed at high temperature and is uncontrolled; Cu(I)-catalyzed atom transfer radical polymerization (ATRP) of VCPs only reaches low conversion. By using N,N-2-naphthyl dihydrophenazine as the PCs, we achieved the first visible-light-regulated ring-opening ATRP of VCPs under mild conditions. A variety of functionalized vinylcyclopropanes were tolerated to afford polymers in high conversions (typically &gt; 90%), and with predictable molecular weight (MW), low dipersities (1.12 – 1.23), and a high degree of linear composition (&gt; 90%). Properties of these obtained polymers, such as high thermal stability and tunable glass transition temperature (Tg), may inspire future applications in material science.

N,N-diaryl dihydrophenazine photoredox catalysts: Applications in efficient ring-opening atom transfer radical polymerization

256th National Meeting (2018)

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