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

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.