Molecular design to increase the photosensitivity of photochromic phenoxyl-imidazolyl radical complexes

Photochromic molecules have received a lot of interest in potential applications. The development of the phenoxyl-imidazolyl radical complex (PIC), which generates two nonequivalent radicals upon light irradiation along with the fast photochemical reaction, is crucial for photoresponsive materials. However, as a novel photochromic compound, the low photosensitivity of PIC derivatives has limited their practical applications. Herein, increased photosensitivity and absorption coefficients of PIC derivatives were achieved while keeping the thermal back reaction rate by introducing the substitution of aryl groups. This strategy gives significant insight into the development of desirable fast photochromic compounds based on the PIC framework.