Fluorescence resonance energy transfer between isomers of molecular photoswitches.

Photocontrollable luminescent molecular photoswitches are pivotal for stimuli-responsive smart materials, yet balancing fluorescence with photoswitching performance and enabling isomerization in solid matrices remain challenging. Herein, we design and synthesize a series of fluorescent donor-acceptor Stenhouse adducts (DASAs) and introduce a strategy utilizing fluorescence resonance energy transfer (FRET) between photoswitch isomers to achieve robust, contactless, and dynamic fluorescence modulation. The resulting DASAs exhibit remarkable photoswitching efficiency and high fluorescence quantum yields. Furthermore, they are successfully incorporated into shape-memory polymer films, which not only facilitate efficient and stable isomerization in the solid state but also enable rapid recovery and reusability. These advantages are leveraged to demonstrate applications in cold-chain transport labeling and multi-level information encryption. This work paves the way for the future design of DASAs and establishes FRET between photoswitch isomers as a powerful concept for developing next-generation photoswitches.