If you have an ACS member number, please enter it here so we can link this account to your membership. (optional)

ACS values your privacy. By submitting your information, you are gaining access to C&EN and subscribing to our weekly newsletter. We use the information you provide to make your reading experience better, and we will never sell your data to third party members.



Acridine radical acts as a powerful photoreductant

Stable organic radical replaces alkali metals or dissolving metal reductants in certain reactions

by Bethany Halford
April 5, 2020 | A version of this story appeared in Volume 98, Issue 13


The structure of a stable acridine radical that acts as a photoreductant.

Reduction, the process of pushing electrons into molecules, is an important transformation for chemical synthesis. But it often requires harsh reagents, like alkali metals, or transformations that can be difficult to scale up, such as reactions that require dissolving metals. Chemists led by the University of North Carolina at Chapel Hill’s David A. Nicewicz have now identified a gentler reagent—an acridine radical (shown), catalytically generated in situ—that can do many of the same reactions when used with ultraviolet light. Nicewicz’s team discovered the photoreductant while working with acridinium salts as photooxidation catalysts. During that work, they found that the acridine radical was indefinitely stable under oxygen-free conditions and had a reduction potential on par with that of elemental lithium. This, the chemists note, makes the acridine radical “one of the most potent chemical reductants reported” (Nature2020, DOI: 10.1038/s41586-020-2131-1). Nicewicz and colleagues used the acridine radical to reduce N-tosyl species, organic bromides, and organic chlorides that can resist reductions. Although there have been a few examples of neutral radicals behaving as compounds that transfer electrons when excited by light, these photoinduced electron-transfer agents are typically transition-metal complexes or closed-shell organic molecules.


This article has been sent to the following recipient:

Chemistry matters. Join us to get the news you need.