Fast and Reversible Humidity-Responsive Luminescent Thin Films

Highly sensitive stimuli-responsive fluorescent films are playing an increasingly important role in the development of smart sensors and erasable optical devices. However, systems involving humidity-responsive fluorescence (HRF) are still very limited compared to those responsive to other common environmental stimuli (e.g., light, heat, pressure, or pH). Herein, by incorporating the 4[4-(dimethylamino)styryl]pyridine chromophore into a polyvinylpyrrolidone host, we have developed new flexible self-supporting nanofiber films that exhibit fast and obvious HRF. The reversible transformation between two fluorescence states can be easily observed and recycled at least 200 times. Fluorescence microscopy images provided in situ evidence of changes in both fluorescence and morphology. This work therefore offers an alternative to conventional humidity sensors based on changes in color and electrical properties. Furthermore, we anticipate that these HRF films can also be employed as optical antiforgery materials.