Europium-Ethyl Acetoacetate Coordination-Modulated Dual Fluorescence Emitting Polymeric Elastomers with Highly Tunable Fluorochromism

A Eu3+-containing elastomer (PAMA-Eu), prepared by copolymerizing acrylic acid, 2-(2-methoxyethoxy)ethyl methacrylate, and 2-(acetoacetoxy)ethyl methacrylate (AAEM), was reported. In this system, the Eu3+ ions and the fluorescent ethyl acetoacetate (EAA) ligand from AAEM serve as dual emission centers, yielding luminescence colors tunable by controlling the Eu3+–EAA coordination. The Fourier transform infrared (FT-IR) analysis confirmed the coordination of Eu3+ ions with the EAA and COOH groups. The change in absorption intensity at larger wavelengths of the UV–vis spectra demonstrates the formation of Eu3+ coordination cross-linking within the polymer network. The EAA ligand as a binding motif on the AAEM monomer is blue-emissive in the absence of Eu3+ ions under 365 nm UV light. A small amount of Eu3+ ions (Eu:AAEM molar ratio ≤0.025:1) can significantly change the emission intensity and the luminescence color of EAA. Upon introducing Eu3+ ions, the luminescence color of the elastomer under 254 nm UV light shifts sequentially from blue to teal, yellow, and ultimately to a Eu3+-dominated red, whereas under 365 nm UV light, the luminescence color changes from blue to teal, green, and finally to yellow. At moderate and high Eu3+ concentrations, the elastomer shows quite different luminescence colors under 254 and 365 nm UV light. This broad and easily tunable fluorescence color enables the application of the PAMA-Eu elastomer in fluorescent anticounterfeiting. By incorporating Tb3+ ions in the PAMA-Eu elastomer, bimodal anticounterfeiting controlled by both excitation wavelength and temperature is achieved. We expect that this coordination-manipulated dual emission center design strategy will provide opportunities for manufacturing anticounterfeiting fluorochromic polymers.