Jstevens

Ultrafast Observation of a Photoredox Reaction Mechanism: Photoinitiation in Organocatalyzed ATRP

Abstract: Photoredox catalysis has driven a revolution in the field of organic chemistry, but direct mechanistic insights into reactions of genuine synthetic utility remain relatively scarce. Herein we report ultrafast time-resolved spectroscopic observation of a bimolecular organocatalyzed photoredox reaction, from catalyst photoexcitation through to photoinduced electron transfer (PET) and intermediate formation, using transient vibrational and…

Synthesis of star polymers using organocatalyzed atom transfer radical polymerization

Abstract: Synthetic routes to higher ordered polymeric architectures are important tools for advanced materials design and realization. In this study, organocatalyzed atom transfer radical polymerization is employed for the synthesis of star polymers through a core-first approach using a visible-light absorbing photocatalyst, 3,7-di(4-biphenyl)-1-naphthalene-10-phenoxazine. Structurally similar multifunctional initiators possessing 2, 3, 4, 6, or 8 initiating…

Visible-Light-Promoted C–S Cross-Coupling via Intermolecular Charge Transfer

Abstract: Disclosed is a mild, scalable, visible-light-promoted cross-coupling reaction between thiols and aryl halides for the construction of C–S bonds in the absence of both transition metal and photoredox catalysts. The scope of aryl halides and thiol partners includes over 60 examples and therefore provides an entry point into various aryl thioether building blocks of…

Strongly Reducing, Visible‐Light Organic Photoredox Catalysts as Alternatives to Precious Metals

Abstract: Photoredox catalysis is a versatile approach for the construction of challenging covalent bonds under mild reaction conditions, commonly using photoredox catalysts (PCs) derived from precious metals. As such, there is need to develop organic analogues as sustainable replacements. Although several organic PCs have been introduced, there remains a lack of strongly reducing, visible‐light organic…

Impact of Light Intensity on Control in Organocatalyzed Atom Transfer Radical Polymerization

Abstract: Organic photoredox catalysts have been shown to operate organocatalyzed atom transfer radical polymerizations (O-ATRP) using visible light as the driving force. In this work, the effect of light intensity from white LEDs was evaluated as an influential factor in control over the polymerization and the production of well-defined polymers. We posit the irradiation conditions…

Organocatalyzed Atom Transfer Radical Polymerization: Perspectives

Abstract: The recent development of organocatalyzed atom transfer radical polymerization (O‐ATRP) represents a significant advancement in the field of controlled radical polymerizations. A number of classes of photoredox catalysts have been employed thus far in O‐ATRP. Analysis of the proposed mechanism gives insight into the relevant photophysical and chemical properties that determine catalyst performance. Discussion…

Photoinduced Organocatalyzed Atom Transfer Radical Polymerization Using Continuous Flow

Abstract: Organocatalyzed atom transfer radical polymerization (O-ATRP) has emerged as a metal-free variant of historically transition-metal reliant atom transfer radical polymerization. Strongly reducing organic photoredox catalysts have proven capable of mediating O-ATRP. To date, operation of photoinduced O-ATRP has been demonstrated in batch reactions. However, continuous flow approaches can provide efficient irradiation reaction conditions and…

Solvent effects on the intramolecular charge transfer character of N,N‐diaryl dihydrophenazine

Abstract: The nature of intramolecular charge transfer (CT) of N,N‐diaryl dihydrophenazine photocatalysts (PCs) in different solvents is explored in context of their performance in organocatalyzed atom transfer radical polymerization (O‐ATRP). PCs having a computationally predicted lowest energy excited state exhibiting CT character can operate a highly controlled O‐ATRP in a wide range of solvent polarities,…

Intramolecular Charge Transfer and Ion Pairing in N,N-Diaryl Dihydrophenazine Photoredox Catalysts

Abstract: Photoexcited intramolecular charge transfer (CT) states in N,N-diaryl dihydrophenazine photoredox catalysts are accessed through catalyst design and investigated through combined experimental studies and density functional theory (DFT) calculations. These CT states are reminiscent of the metal to ligand charge transfer (MLCT) states of ruthenium and iridium polypyridyl complexes. For cases where the polar CT…

Organocatalyzed Atom Transfer Radical Polymerization Using N-Aryl Phenoxazines

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…