Visualization of Biogenic Amines and In Vivo Ratiometric Mapping of Intestinal pH by AIE‐Active Polyheterocycles Synthesized by Metal‐Free Multicomponent Polymerizations

Acid‐base homeostasis is crucial for normal physiology, metabolism, and functions of living organisms. Thus, the development of effective techniques to monitor it either in vitro or in vivo is in great demand. Herein, a series of multifunctional oxazine‐containing polyheterocycles with aggregation‐induced emission characteristics are in situ generated by metal‐free one‐pot A 3 polymerizations of terminal diynes, dialdehydes, and ureas. Most of the polymers are synthesized with high molecular weights ( M w up to 49 900) in nearly quantitative yields and display intense solid‐state emission and remarkable fluorescence response to protonation and deprotonation. Based on the unique photophysical properties, a fast responsive and reversible fluorescent sensor for ammonia with a detection limit of 960 ppb is achieved and applied for detecting biogenic amines and seafood spoilage. Besides, the polymeric nanoparticles show excellent lysosome‐targeting specificity in cell imaging. The polyheterocycles show ratiometric pH sensing behavior with a broad acid‐base response window from pH 1 to 9, which shed light on visualizing physiologic pH in gastrointestinal tract. Taking freshwater Cladocera Moina macrocopa as a model organism, in vivo mapping of its intestinal pH shows an increased pH gradient approximately from 4.2 to 7.8 along the foregut, midgut, and hindgut.