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Abstract Phenoxazines are a successful class of organic photoredox catalysts (PCs) with tunable redox and photophysical properties. Originally, we aimed to realize more reducing phenoxazine PCs through heteroatom core substituted (HetCS) derivatives, while maintaining an efficiently oxidizing PC^·+. However, core modification with thioether or ether functionality to a PC that exhibits photoinduced intramolecular charge transfer (CT) negligibly alters the singlet excited state reduction potential (E_S1°*), while yielding a less oxidizing PC^·+(E_1/2) (E_1/2 = 0.50–0.64 V vs. SCE) compared to the noncore modified PC1(0.68 V vs. SCE). Photophysical characterization of HetCS PCs revealed that increasing electron density on the core of a CT exhibiting PC stabilizes the emissive state and PC^·+, resulting in a relatively unchangedE_S1°* compared to PC1. In contrast, modifying the core of a PC that does not exhibit CT yields a highly reducingE_S1°* (PC3= −2.48 V vs. SCE) compared to its CT equivalent (PC1d= −1.68 V vs. SCE). The impact of PC property on photocatalytic ability was evaluated through organocatalyzed atom transfer radical polymerization (O‐ATRP). HetCS PCs were able to yield poly(methyl methacrylate) with low dispersity and moderate targeted molecular weight as evaluated by initiator efficiency (I*) in DMAc (Ð= 1.20–1.26;I*= 47–57%). Ultimately, this work provides insight into how phenoxazine PC properties are altered through structural modification, which can inform future PC design. 

Abstract Herein, we describe a new strategy for the carbonylation of alkyl halides with different nucleophiles to generate valuable carbonyl derivatives under visible light irradiation. This method is mild, robust, highly selective, and proceeds under metal‐free conditions to prepare a range of structurally diverse esters and amides in good to excellent yields. In addition, we highlight the application of this activation strategy for¹³C isotopic incorporation. We propose that the reaction proceeds by a photoinduced reduction to afford carbon‐centered radicals from alkyl halides, which undergo subsequent single electron‐oxidation to form a carbocationic intermediate. Carbon monoxide is trapped by the carbocation to generate an acylium cation, which can be attacked by a series of nucleophiles to give a range of carbonyl products. 

Abstract Herein, we report a selective photooxidation of commodity postconsumer polyolefins to produce polymers with in‐chain ketones. The reaction does not involve the use of catalyst, metals, or expensive oxidants, and selectively introduces ketone functional groups. Under mild and operationally simple conditions, yields up to 1.23 mol % of in‐chain ketones were achieved. Installation of in‐chain ketones resulted in materials with improved adhesion of the materials and miscibility of mixed plastics relative to the unfunctionalized plastics. The introduction of ketone groups into the polymer backbone allows these materials to react with diamines, forming dynamic covalent polyolefin networks. This strategy allows for the upcycling of mixed plastic waste into reprocessable materials with enhanced performance properties compared to polyolefin blends. Mechanistic studies support the involvement of photoexcited nitroaromatics in consecutive hydrogen and oxygen atom transfer reactions. 

Photoredox catalysis driven by visible light has improved chemical synthesis by enabling milder reaction conditions and unlocking distinct reaction mechanisms. Despite the transformative impact, visible-light photoredox catalysis remains constrained by the thermodynamic limits of photon energy and inefficiencies arising from unproductive back electron transfer, both of which become particularly pronounced in thermodynamically demanding reactions. In this work, we introduce an organic photoredox catalyst system that overcomes these obstacles to drive chemical transformations that require super-reducing capabilities. This advancement is accomplished by coupling the energy of two photons into a single chemical reduction, whereas inefficiencies from back electron transfer are mitigated through a distinct proton-coupled electron transfer mechanism embedded in the catalyst design. The super-reducing capabilities of this organic catalyst system are demonstrated through efficient application in a broad scope of challenging arene reductions.