Long-standing radical species have raised noteworthy concerns in organic functional chemistry and materials for years. Thus far, the generation of the stable radicals has largely relied on a redox reaction or a thermal process, lacking the convenience from the perspective of material manipulation. If we can achieve stable radicals by light, the preparation and control can be precise and rapid, and manipulation can also be done remotely without direct sample contact. Although it is popular to employ photon (or photothermal effect) to generate intermediate radicals for reactions, to straightforwardly produce stable radical species by light, which will be in favor of further developing photochemical methodology as well as for steady-state material application, is extremely desirable but challenging.

To address the above-mentioned issue, Zhu’s group at Fudan University, collabrated with Zou’s group at Shanghai University of Electric Power, presented a photochromism triggering strategy for preparing stable radical species by light. By designing and constructing a a pyrrole and chloride assisted photochromic structure, they found a photochemical process accompanied by a simultaneous production and stabilization of a radical species. Theoretical study and mechanism construction indicate the photochromism embedded π-system can provide a superior spin-delocalization effect and a large steric effect, mostly avoiding possible consumptions and making the radical stable for hours even under an oxygen-saturated condition. Moreover, the ultrastable radical system can be applied for visualized and quantitative detection towards ozone, the excessive production of which can raise potent environmental issues near the ground level. As such a detection, which can be even transferred to a portable gel material, relies on a radical capturing mechanism, a higher sensing rate can be achieved compared to traditional redox techniques for peroxide detection.

The work not only provides a paradigm of applying light into the production of stable radical characteristic, but also may pave a new way for the future development of photoreaction methodology and photomanipulation of advanced optoelectronic materials. The related paper has been published in Nature Communications, with Mr. Xuanying Chen in the group as the first author. 
See details: Xuanying Chen, Wandong Zhao, Gleb Baryshnikov, Michael L. Steigerwald, Jian Gu, Yunyun Zhou, Bin Wu, Hongwei Wu, Hans ?gren, Qi Zou*, Wenbo Chen*, Liangliang Zhu*, Engineering Stable Radicals Using Photochromic Triggers, Nat. Commun. 2020, 11, 945