A multi-stimuli responsive Salicylaldehyde Hydrazone with high-contrast chromic behaviors, tetracycline sensing and...

Stimuli-responsive materials have garnered significant attention due to their wide applications in sensors, information encryption, and intelligent optoelectronic devices. However, developing intelligent responsive materials based on a single molecule that can achieve high contrast with diverse responses to multiple external stimuli remains a challenge. Herein, a salicylaldehyde hydrazone (H₃L), was synthesized via a solvothermal method. H₃L exhibited reversible multi-stimuli-responsive behaviors, including mechanochromism, photochromism, and acidochromism. Specifically, H₃L exhibits obvious responses in color and luminescence upon multi-stimuli. Mechanical grinding triggers distinct color changes from yellow to orange under ambient light, accompanied by a 40 nm bathochromic shift in fluorescence (from yellow-green to yellow), which can be restored via ethanol vapor fumigation. Upon ultraviolet irradiation, H₃L exhibits photochromism and photoswitchable luminescence, turning to orange under ambient light and its luminescence turning to beige in the solid state, with restoration achieved by heating or storage in the dark. Similar photo-responsive behavior is also observed in solution. H₃L also displays acid-responsive behavior, upon exposure to TFA vapor, the color and luminescence turn to brown and reddish-brown (from 500 nm to 675 nm, 175 nm bathochromic shift), respectively. It can also be restored under the TEA fumigation. Furthermore, H₃L showed "turn-off" fluorescent sensing of tetracycline (TC) with satisfactory sensitivity, selectivity, and low limits. Leveraging the multi-stimuli-responsive characteristics, H₃L and its PMMA-based flexible film were applied to multi-level dynamic information encryption and anti-counterfeiting. This work provides a robust strategy for the design of multi-stimuli-responsive materials.