Light-induced reversible switching of generation and extinction of an organic radical anion.

Radicals play a crucial role across various domains, ranging from serving as catalysts in chemical reactions to materials for spintronic applications. Currently, a major challenge for the chemists is the development of the next generation of organic radicals controllable by photons. To tackle this challenge, here we introduce a dyad system that combines a dimethyldihydropyrene (DHP) photochromic unit with a naphthalene diimide (NDI) moiety. This system forms a stable organic NDI-based radical-anion upon exposure to light in a solvent containing a small amount of an amine that acts as an electron donor. The radical anion formation has also been demonstrated with a chemical reductant. The photoisomerization of this photochromic system converts it into a less-conjugated and less-electron-rich form, affecting the generation of the radical as well as its stability. Consequently, light-induced isomerization effectively quenches the radical. Thus, the formation and existence of the radical can be adjusted by manipulating the photoisomerization of the photochromic unit under diverse light sources. Additionally, the system exhibits significant differences in emission in the radical and the closed-shell state, thereby offering a dual readout of the state of the molecule.