Single‐Component Photochromic Smart Semiconductor with Photoswitchable Fast Bidirectional Electron Transfer

Abstract Introduction of photochromic properties into semiconductors confers semiconductors with smart behaviors, color‐related applications, and new modulation approaches. Photochromophores with electron‐transfer (redox) behavior, such as viologen and naphthalene diimide, are ideal functional motifs to design photochromic semiconductors owing to good adaptability to the solid matrix, but their reverse reactions are exclusively realized by the thermal mode, which is slow (in dozens of seconds or longer) and thus significantly hinders real applications in the fields that require high‐speed switching. This study reveals that photoexcitation in the electronic absorption band of the π‐aggregate of viologen cation radicals can successfully trigger reverse electron transfer quickly (in 1 s with a continuous‐wave 808 nm laser at a power density of 5 W cm −2 ; the photothermal effect is excluded), and the first single‐component all‐optically photochromic semiconductor is accordingly discovered. This discovery breaks through a traditional concept that reverse reactions of viologen compounds can not be triggered by the light, and provides a potential approach to realize all‐optical switch of single‐component photochromic smart semiconductors based on electron‐transfer photochromic functional motifs.