Organocatalyzed Atom Transfer Radical Polymerization Using N-Aryl Phenoxazines as Photoredox Catalysts

Abstract

N-Aryl phenoxazines have been synthesized and introduced as strongly reducing metal-free photoredox catalysts in organocatalyzed atom transfer radical polymerization for the synthesis of well-defined polymers. Experiments confirmed quantum chemical predictions that, like their dihydrophenazine analogs, the photoexcited states of phenoxazine photoredox catalysts are strongly reducing and achieve superior performance when they possess charge transfer character. We compare phenoxazines to previously reported dihydrophenazines and phenothiazines as photoredox catalysts to gain insight into the performance of these catalysts and establish principles for catalyst design. A key finding reveals that maintenance of a planar conformation of the phenoxazine catalyst during the catalytic cycle encourages the synthesis of well-defined macromolecules. Using these principles, we realized a core substituted phenoxazine as a visible light photoredox catalyst that performed superior to UV-absorbing phenoxazines as well as previously reported organic photocatalysts in organocatalyzed atom transfer radical polymerization. Using this catalyst and irradiating with white LEDs resulted in the production of polymers with targeted molecular weights through achieving quantitative initiator efficiencies, which possess dispersities ranging from 1.13 to 1.31.

Intramolecular Charge Transfer and Ion Pairing in N,N-Diaryl Dihydrophenazine Photoredox Catalysts for Efficient Organocatalyzed Atom Transfer Radical Polymerization

“…For example, theoretical insight led to the discovery of a core substituted N -aryl phenoxazine as an efficient visible light organic PC for the O-ATRP for the synthesis of poly(methyl methacrylate) (PMMA) with tailored molecular weights (MWs) and low Đ while achieving high initiator efficiencies (I*s). 20 …”

Photoinduced Organocatalyzed Atom Transfer Radical Polymerization Using Continuous Flow

“…Recently, our group has revealed N,N -diaryl dihydrophenazines 19 and N -aryl phenoxazines, 20 as strongly reducing visible-light-absorbing PCs efficient for O-ATRP. Mechanistic studies of O-ATRP mediated by N -aryl-phenothiazine catalysts highlighted the necessity for fast activation and deactivation for controlled polymerizations.…”

Endo and Exo Diels–Alder Adducts: Temperature-Tunable Building Blocks for Selective Chemical Functionalization

“…The choice of photocatalyst was based on optimal compatibility with the initiator-type as demonstrated in previous reports. 19,20 This represents the first copolymer ( P2 ) to contain both endo and exo isomers (Figure 4a). The addition of BnMA serves as a covalently bound internal 1 H NMR reference to facilitate reliable determination of the efficiency of selective deprotection.…”