Multistimuli Responsive Solid-State Emission of a Zinc(II) Complex with Multicolour Switching.

The development of smart luminescent materials, especially those stimulus-responsive fluorescent materials that can switch between different colors repeatedly under external stimulation based on a single molecule, is of great significance but a challenge. In this work, a novel zinc(II)-Schiff base complex (ZnL) was obtained and characterized. Upon exposure to the HCl and NH vapors, it displayed remarkable tricolor acidochromic behavior with high contrast and rapid response under the ambient light as well as UV light (365 nm). The XPS analyses of ZnL crystals before and after HCl/NH fuming show that the acidochromism originates principally from the adsorption of vapor and the gas-solid reaction equilibrium on the crystal surface. The reddish-brown color of the HCl-fumigated ZnL crystals could be attributed to the generation of HL at the surface of ZnL, and red-shifted emission could be ascribed to the self-absorption effect. The single crystal X-ray diffraction data indicate that these processes cause slight changes in the molecular conformation and crystal packing. ZnL shows reversible mechanochromic luminescence behavior between yellow and orange emission during the grinding-fuming/heating cycles due to the modulation between amorphous and crystalline states. Moreover, ZnL was successfully made into test paper for the rapid detection of HCl/NH vapors and mechanical stimuli.