Naphthalenediimide-based photochromic MOFs: Structure visualization upon radical formation, and applications in purple light detection, inkless printing and anti-counterfeiting

It is still a great challenge to understand the structural variation during the photochromic process, to rationally regulate the photochromic performance, and to expand the practical application of NDI-based photochromic materials. Herein, we found a 2D NDI-type photochromic MOF (1). When illuminated by 395 nm purple light, 1 underwent a single-crystal-to-single-crystal (SCSC) transition, resulting in 1-P, which is a rare structural visualization phenomenon during the formation of free radicals. In addition, it was demonstrated for the first time that the introduction of solvent molecules into the system (1@MeCN) can modulate the photochromic ability caused by electron transfer. It was found that 1 and 1@MeCN have the most sensitive response to 395 nm purple light, and are ideal candidates for detecting and filtering purple light. Finally, a photochromic glass based on 1@MeCN was reported, which is first applied in ink-free printing, purple light detection/filtering, and information anti-counterfeiting.