Dimethyl Dihydroacridines as Photocatalysts in Organocatalyzed Atom Transfer Radical Polymerization of Acrylate Monomers

Abstract

Development of photocatalysts (PCs) with diverse properties has been essential in the advancement of organocatalyzed atom transfer radical polymerization (O‐ATRP). Dimethyl dihydroacridines are presented here as a new family of organic PCs, for the first time enabling controlled polymerization of challenging acrylate monomers by O‐ATRP. Structure–property relationships for seven PCs are established, demonstrating tunable photochemical and electrochemical properties, and accessing a strongly oxidizing 2PC.+ intermediate for efficient deactivation. In O‐ATRP, the combination of PC, implementation of continuous‐flow reactors, and promotion of deactivation through addition of LiBr are critical to producing well‐defined acrylate polymers with dispersities as low as 1.12. The utility of this approach is established through demonstration of the oxygen‐tolerance of the system and application to diverse acrylate monomers, including the synthesis of well‐defined di‐ and triblock copolymers.

Aryl dechlorination and defluorination with an organic super-photoreductant

“…−3.4 V vs. SCE can be estimated for the singlet excited state, which is an exceptionally high value in comparison to most known photoreductants. [3][4][5][6][7][8][9][10][11][12][13][14][15][16] However, acetone is reduced at a potential of −2.84 V vs. SCE, 73 whereas benzene reduction necessitates a potential of −3.42 V vs. SCE, 74 hence photoexcited TDAE is readily able to reduce acetone, whereas benzene reduction should be much more challenging. Indeed, the fluorescence of TDAE in cyclohexane is quenched by acetone with essentially diffusion-limited kinetics (Fig.…”

“…Photochemistry has become remarkably popular, and numerous classes of chemical reactions can now be driven by visible light. 1,2 Recently, there has been significant interest in developing photosensitizers that are able to provide very high reducing power, [3][4][5][6][7][8][9][10][11][12][13][14][15][16] in order to perform ever more thermodynamically challenging reactions. [17][18][19] At the same time, new multi-photon excitation concepts that rely on the pooling of two visible photons to access highly reducing intermediates have been developed.…”

Metal-free atom transfer radical polymerization: reaching ppm catalyst loading under sunlight

“…Notably, the y-intercept of the number average molecular weight (Mn) versus conversion plot was 870 Da, suggesting the control of the polymerization was achieved after the initial addition of ~6 MMA (Figure 3c). 24 This strict control may benefit from a more efficient deactivation process 25,35,43 due to the radical cations of ODA photocatalysts possessing a better oxidizing ability.…”

“…It is worth mentioning that acrylate monomers proved to be very challenging to achieve a controlled polymerization with low dispersity by O-ATRP methods due to their high polymerization rate. 24,26,43 To our delight, this control on low dispersity is even better than that with dihydroacridine photocatalysts which were developed especially for this type of monomers very recently. 43 In addition, ODA photocatalysts could also mediate the reversible addition-fragmentation chain transfer (RAFT) polymerization [48][49][50] of MMA at low ppm catalyst loading (1-10 ppm) under sunlight, with excellent control and narrow dispersity (Đ < 1.10, entries [15][16][17], which are comparable to the precious iridium photocatalyst 51 (Supplementary Table 7).…”

“…Notably, ODA 5d also represent a rare example of organic photocatalysts that could promote the polymerization of both MMA and BA, as well as RAFT polymerization of MMA with good controls. 43,49 In summary, a catalyst design logic based on heteroatom-doping of polycyclic arenes has been successfully introduced into the development of new photocatalysts for organocatalyzed atom transfer radical polymerization (O-ATRP). Oxygen-doped antratherene (ODA) has been identified as a novel catalyst framework with unprecedented high efficiency, featuring its strong visible light absorption and excellent performance at extremely low catalyst loadings in both organocatalyzed ATRP and RAFT polymerization.…”