The transition metal-catalyzed C-H functionalization with hydroxylamine derivatives serving as both reactants and internal oxidants has attracted a lot of interest. These reactions obviate the need for external oxidants and therefore result in high reactivity and selectivity, as well as excellent functional group tolerance under mild reaction conditions, and moreover, water, methanol or carboxylic acid is generally released as the by-product, thus leading to reduced waste. This review focuses on the transition metal-catalyzed oxidative C-H functionalization of N-oxyenamine internal oxidants, with an emphasis on the scope and limitations, as well as the mechanisms of these reactions.

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An efficient near-infrared (NIR) quantum-cutting (QC), involving the emission of two low-energy NIR photons from an absorbed visible photon via a cooperative downconversion mechanism in GdBO3:Tb3+,Yb3+ nanophosphors, has been demonstrated. Upon excitation of Tb3+ with a visible photon at 486nm, two NIR photons could be emitted by Yb3+ through cooperative energy transfer from Tb3+ to two Yb3+ ions. The dependence of Yb3+ doping concentration on the visible and NIR emissions, decay lifetime, and quantum efficiencies from the QC phosphors has been investigated. Calculations indicate that the optimal NIR quantum efficiency approaches 182% before reaching concentration quenching threshold. Application of the QC nanophosphors in silicon-based solar cells might greatly enhance its response.

Radical addition is a robust tool for bond formation. While ketyl radical reactivity of aldehydes by photoredox has been wellestablished, herein, we have now revealed a pathway for umpolung addition of aldehydes with or without external reductant. Hence, the reductive alkylations and challenging benzylations of nitrogen heteroarenes (i.e., Minisci reactions) are enabled by the bromidepromoted visible light-mediated photocatalysis. The present protocol offers a mild, viable method for late-stage alkylations and transitionmetal-free benzylations of biologically active nitrogen-heteroarene molecules. Mechanistic studies are indicative of a bromide-initiated acyl radical mechanism in the absence of external reductant.