Synthesis and Fluorescence Properties of Divalent Europium‐Poly(Methacrylate Containing Crown Ether Structure) Complexes

Abstract

Divalent europium complexes with poly(methacrylate containing crown ether structure)s, “poly(crown ether)s,” were prepared and their fluorescence properties studied. The polymers used were poly(15‐crown‐5‐methyl methacrylate) (PMA15C5), copoly(15‐crown‐5‐methyl methacrylate‐ X) [copoly(MA15C5‐ X)]; [ X =MMA, EMA, BMA, 2‐methoxyethyl methacrylate (MAGI), 3,6,9,12,15‐pentaoxahexadecyl methacrylate (MAG5)], poly(18‐crown‐6‐methyl methacrylate) (PMA18C6), and copoly(18‐crown‐6‐methyl methacrylate‐MMA) [copoly(MA18C6‐MMA)], which were obtained by bulk polymerization. The fluorescence properties of Eu2+ polymers activated by complexing Eu2+ ions with crown ether groups were measured in powder form. The Eu2+‐poly(crown ether)s irradiated by UV light generally gave blue bright emission in the region of 420–465 nm. It was Eu2+‐copoly(MA15C5‐ X); (X =MMA, EMA, and MAG1) that showed the largest emission intensity among the Eu2+ polymers, and its emission intensity was ca. 20% of that for (NBS1026) whose quantum efficiency is about 76%. The intensities of emissions for the Eu2+ polymers containing 15‐crown‐5 were much larger than that for the ones containing 18‐crown‐6. This was the same result as obtained in the studies on the Eu2+ monomeric crown ether complexes in a methanol solution. The increasing order of the maximum emission intensities for the Eu2+polymers containing 15‐crown‐5 was found to be Eu2+‐copoly(MA15C5‐MMA), Eu2+‐copoly(MA15C5‐EMA), Eu2+‐copoly (MA15C5‐MAG1) > Eu2+‐copoly(MA15C5‐BMA) > Eu2+‐PMA15C5 > Eu2+‐copoly(MA15C5‐MAG5). In the case of polymers containing 18‐crown‐6, the intensity was a little larger for the Eu2+ homopolymer than for the Eu2+ copolymer. The value of the luminescence lifetime, τ, for the Eu2+‐poly(crown ether)s was in a range of ca. 300–500 ns at the optimal concentration. These polymer systems showed concentration quenching and there were supposed to be two kinds of concentration quenching, one is responsible for the Eu2+‐Eu2+ distance and another is due to a structural change in the complex, by the studies on the dependence of the emission intensities and luminescence lifetimes on the concentration. The Eu2+ ion in the solid Eu2+ copolymer complexes exhibited fairly better stability to air than the Eu2+ ion due to complexing with the monomeric crown ethers in a methanol solution.