Multiple stimuli-responsive properties of Coumarin-Salicylaldehyde Schiff Bases

Organic small-molecules of multiple stimuli-responses were widely paid attention, which can be applied in multiple fields simultaneously, such as thermal sensor, force response, pH probe, reagents for the detection of metal ion and so forth. In the present work, three novel coumarin derivatives (XDS-R) were synthesized from various salicylaldehydes containing different substituents (R = H, Cl, Br), following by investigations about their multiple stimuli-responsive properties concerning aggregation-induced emission (AIE), mechanochromism, thermochromism and pH response. Single crystals of XDS-R indicate that intramolecular hydrogen bonds cause the restriction of intramolecular vibration, leading to AIE character and mechanochromic property. Interestingly, two substituents (H, Cl) have little effect on fluorescence intensity and color, and whereas have distinguishable influences on functionalized fluorescence response. In the pH range of 2.00–8.00, only XDS-H exhibited regular pH-response, while XDS-Cl and XDS-Br showed excellent pH tolerance. Mechanochromic XDS-R is able to recover to original state under heating. A simple multilevel anticounterfeit label was made by the combination of XDS-Cl and previous-reported DDHAC without an automatic heat-inspired recovery. Combined multilevel stimuli-responsive material of XDS-Cl and previous DDHAC displayed potential application of anti-counterfeiting mark.