Programmable Multi-State Fluorescence Switching on a Dynamic Molecular System via Sequential Dynamic Covalent Chemistry and Applications

Dynamic molecular systems capable of controlled transformations are foundational for developing next-generation intelligent materials and sensors. However, achieving sequential, multistate switching with distinct optical outputs on a single molecular platform remains challenging. Here, we introduce a class of dynamic fluorescent systems built upon a single benzo-conjugated acceptor. This system undergoes programmed molecular reconfiguration and fluorescence switching through sequential chemical and pH-driven triggers, leveraging intramolecular oxa/thiol-Michael addition-elimination reactions via dynamic covalent bonding in aqueous medias. Each distinct molecular state exhibits unique, trackable absorbance and fluorescence signatures, governed by precisely controlled pseudo-p<i>K</i> _a values. We demonstrate the utility of this system by achieving real-time, noninvasive optical tracking of topological transitions in soft materials, specifically monitoring hydrogel degradation and reformation (gel-sol-gel). Furthermore, by tuning the molecular scaffold, we developed derivatives for live-cell imaging, enabling dynamic visualization of intracellular pH fluctuations. This work presents a versatile platform for designing programmable, multistimuli-responsive molecular systems with potential in adaptive materials, chemical sensing, and advanced biomedical diagnostics.