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 thus enable increased polymerization performance. Herein, the adaptation of O-ATRP to a continuous flow approach has been performed with multiple visible-light absorbing photoredox catalysts. Using continuous flow conditions, improved polymerization results were achieved, consisting of narrow molecular weight distributions as low as 1.05 and quantitative initiator efficiencies. This system demonstrated success with 0.01% photocatalyst loadings and a diverse methacrylate monomer scope. Additionally, successful chain-extension polymerizations using 0.01 mol % photocatalyst loadings reveal continuous flow O-ATRP to be a robust and versatile method of polymerization.

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 sites were used in this study for the synthesis of linear telechelic polymers and star polymers typically possessing dispersities lower than 1.5 while achieving high initiator efficiencies. Furthermore, no evidence of undesirable star-star coupling reactions was observed, even at high monomer conversions and high degrees of polymerization. The utility of this system is further exemplified through the synthesis of well-defined diblock star polymers.

The use of low-energy deep-red (DR) and near-infrared (NIR) light to excite chromophores enables catalysis to ensue across barriers such as materials and tissues. Herein, we report the detailed photophysical characterization of a library of OsII polypyridyl photosensitizers that absorb low-energy light. By tuning ligand scaffold and electron density, we access a range of synthetically useful excited state energies and redox potentials.1 Introduction1.1 Scope1.2 Measuring Ground-State Redox Potentials1.3 Measuring Photophysical Properties1.4 Synthesis of Osmium Complexes2 Properties of Osmium Complexes2.1 Redox Potentials of Os(L)2-Type Complexes2.2 Redox Potentials of Os(L)3-Type Complexes2.3 UV/Vis Absorption and Emission Spectroscopy3 Conclusions

Photoredox catalysis has revolutionized synthetic chemistry in recent decades. However, the field has traditionally used high-energy blue/ultraviolet light to activate chromophores. High-energy irradiation is associated with several drawbacks (e.g., activation of sensitive functional groups, undesired metal-ligand homolysis, background activation of molecules, and poor penetration), which has led researchers to develop alternative systems with lower energy deep red (DR) or near-infrared (NIR) light. This graphical review provides a concise overview of photophysical principles relevant to photoredox catalysis. Several applications that benefit from low-energy irradiation, such as large-scale batch reactions, photodynamic therapy, biological labeling, and multi-photon excitation are reviewed.

Photocatalysis driven by visible and ultraviolet irradiation is a fundamental tool for synthetic chemists. Recently, expansion of this tool to near-infrared (NIR) light has gained in popularity. Herein, we report the detailed photophysical characterization of a library of OsII polypyridyl photosensitizers that absorb NIR irradiation. By tuning ligand scaffold and electron density, we access a range of synthetically useful excited state energies and redox potentials.

Photocatalysis driven by visible and ultraviolet irradiation is a fundamental tool for synthetic chemists. Recently, expansion of this tool to near-infrared (NIR) light has gained in popularity. Herein, we report the detailed photophysical characterization of a library of OsII polypyridyl photosensitizers that absorb NIR irradiation. By tuning ligand scaffold and electron density, we access a range of synthetically useful excited state energies and redox potentials.