The Birch reduction is a powerful synthetic methodology that uses solvated electrons to convert inert arenes to 1,4-cyclohexadienesvaluable intermediates for building molecular complexity. Birch reductions traditionally employ alkali metals dissolved in ammonia to produce a solvated electron for the reduction of unactivated arenes such as benzene (E red < −3.42 V vs SCE). Photoredox catalysts have been gaining popularity in highly reducing applications, but none have been reported to demonstrate reduction potentials powerful enough to reduce benzene. Here, we introduce benzo­[ghi]­perylene imides as new organic photoredox catalysts for Birch reductions performed at ambient temperature and driven by visible light from commercially available LEDs. Using low catalyst loadings (<1 mol percent), benzene and other functionalized arenes were selectively transformed to 1,4-cyclohexadienes in moderate to good yields in a completely metal-free reaction. Mechanistic studies support that this unprecedented visible-light-induced reactivity is enabled by the ability of the organic photoredox catalyst to harness the energy from two visible-light photons to affect a single, high-energy chemical transformation.

Photoinduced organocatalyzed atom-transfer radical polymerization (O-ATRP) is a controlled radical polymerization methodology that can be mediated by organic photoredox catalysts under the influence of light. However, typical O-ATRP systems require relatively high catalyst loadings (1000 ppm) to achieve control over the polymerization. Here, new core-extended diaryl dihydrophenazine photoredox catalysts were developed for O-ATRP and demonstrated to efficiently operate at low catalyst loadings of 5-50 ppm to produce polymers with excellent molecular weight control and low dispersity, while achieving near-quantitative initiator efficiency. Photophysical and electrochemical properties of the catalysts were computationally predicted and experimentally measured to correlate these properties with improved catalytic performance. Furthermore, these catalysts were utilized to synthesize materials with complex architectures, such as triblock copolymers and star polymers. To demonstrate their broad utility, polymerizations employing these catalysts were successfully scaled up to 5 g and revealed to efficiently operate under air.

The structure and activity of proteins is the gold standard for functional polymeric materials. This highlight seeks to calibrate the reader with respect to recent attempts to mimic the various structural and functional traits of proteins using the techniques of modern polymer chemistry. From advances in sequence-controlled polymers (primary structure), to peptidomimetics, foldamers, single-chain nanoparticles (secondary and tertiary structure), accessing the various structural aspects of protein chemistry is a vibrant research area. Likewise, the properties and utility of proteins in applications such as catalysis and molecular recognition are being emulated in the laboratory to great effect. Rather than provide an exhaustive review on any one of these topics, this article seeks to highlight the common thread among them, encouraging discussion and collaboration that will result in the next generation of smart materials with advanced structure and function.

Investigation of the effects of a solvent on the photophysical and redox properties of the photoredox catalyst (PC), N,N-di­(2-naphthyl)-5,10-dihydrophenazine (PC 1), revealed the opportunity to use tetrahydrofuran (THF) to modulate the reactivity of PC 1 toward achieving a controlled organocatalyzed atom transfer radial polymerization (O-ATRP) of acrylates. Compared with dimethylacetamide (DMAc), in tetrahydrofuran (THF), PC 1 exhibits a higher quantum yield of intersystem crossing (ΦISC = 0.02 in DMAc, 0.30 in THF), a longer singlet excited-state lifetime (τSinglet = 3.81 ns in DMAc, 21.5 ns in THF), and a longer triplet excited-state lifetime (τTriplet = 4.3 μs in DMAc, 15.2 μs in THF). Destabilization of 1 •+ , the proposed polymerization deactivator, in THF leads to an increase in the oxidation potential of this species by 120 mV (E 1/2 0 = 0.22 V vs SCE in DMAc, 0.34 V vs SCE in THF). The O-ATRP of n-butyl acrylate (n-BA) catalyzed by PC 1 proceeds in a more controlled fashion in THF than in DMAc, producing P­(n-BA) with low dispersity, Đ (Đ < 1.2). Model reactions and spectroscopic experiments revealed that two initiator-derived alkyl radicals add to the core of PC 1 to form an alkyl-substituted photocatalyst (2) during the polymerization. PC 2 accesses a polar CT excited state that is ∼40 meV higher in energy than PC 1 and forms a slightly more oxidizing radical cation (E 1/2 0 = 0.22 V for 1 •+ and 0.25 V for 2 •+ in DMAc). A new O-ATRP procedure was developed wherein PC 1 is converted to 2 in situ. The application of this method enabled the O-ATRP of a number of acrylates to proceed with moderate to good control (Đ = 1.15–1.45 and I* = 83–127%).

<p>The Birch reduction is a powerful synthetic methodology that uses solvated electrons to convert inert arenes to 1,4-cyclohexadienes—valuable intermediates for building molecular complexity. This reaction historically requires dangerous alkali metals and cryogenic liquid ammonia as the solvent, severely limiting application potential and scalability. Here, we introduce benzo[ghi]perylene imides as new organic photoredox catalysts for Birch reductions performed at ambient temperature and driven by visible light. Using low catalyst loadings (<1 mole percent), benzene and other functionalized arenes can be selectively transformed to 1,4-cyclohexadienes in good yields. Mechanistic studies support that this unprecedented visible light induced reactivity is enabled by the ability of the organic photoredox catalyst to harness the energy from two visible light photons to affect a single, high energy chemical transformation, likely proceeding through a solvated electron.</p>