Harnessing interfacial click polymerization using pyridinium-yne films as photochromic, radical generation and sensing platforms

Convenient and effective fabrication of free-standing organic polymer films with tunable properties is highly desirable towards visual sensing applications. Herein, we pioneered an innovative interfacial pyridinium-yne click polymerization strategy to in situ fabricate uniform, defect-free, and large-area films. Using pyridinium salt (HDPP-BF4) as an acceptor and tricarbonylbenzene activated alkyne (TFB-3EK) as a donor, a free-standing HDPP-TFB-BF4 film (Film #1) with precisely tunable thickness from tens to hundreds of nanometers was formed at the air-DMSO interface. Interestingly, Film #1 exhibited promising photochromism, showing a 100 nm hypsochromic shift and a 5-fold fluorescence enhancement under continuous UV irradiation, which induced the formation of a radical-based Film #2. Film #2 served as a portable visual sensing platform for gaseous ammonia, achieving a detection limit as low as 0.16 ppm, and was successfully applied as a colorimetric chart for seafood spoilage. Strategically, an anion exchange of Film #2 with TCNQ- yielded a fluorescence-silent Film #3, which enabled efficient detection and elimination of reactive oxygen species through turn-on fluorescence visualization. This work not only provides a straightforward approach for in situ fabricating versatile polymer films but also establishes a generalizable strategy for developing multi-responsive visualization systems through the rational molecular design and controlled polymer variability. Designing organic polymers for visual sensing is highly desirable, yet tuning their properties remains challenging. Here, the authors report interfacial click polymerized pyridinium-yne films that exhibit photochromism, radical generation, and sensing properties.