Synthesis And Properties Of The Highly Luminescent Bonding-type Rare Earth Polymer

The rare earth polymer materials have attracted considerable interests for their good luminescent characteristics, high color purity of rare earths and the excellent processability of polymers. The bonding-type rare earth polymers in which the lanthanide complexes are covalently bound in the main chain would cause the lanthanide complexes to distribute evenly in the polymer marixes, and could still maintain the luminescence intensity when the rare earth metal content is high. Furthermore, the luminescence intensities of the polymers increase linearly with an increase in the rare earth content. Up to now most of the approaches to bind a lanthanide complex to a polymer backbone take advantage of a polymerizable ligand such as acrylic acid. But it should be noted that the acrylic acid ligand makes little contribution to the luminescence of the complexes, and occupies the coordination number of rare earth ions, which would significantly affect the luminescence properties of the polymers. This thesis aims to synthesize highly luminescent rare earth polymers through the design of multifunctional ligands, and to develop the synthesis and preparation methods for the rare earth polymer luminescent materials with high performance. The following results have been achieved:1) Two multi-functional ligands,5-acrylamido-1,10-phenanthroline (Aphen) and 5-acryloxyethoxymethyl-8-hydroxyquinoline (Hamq), were designed and synthesized, and their synthesis processes were optimized. Our design is based upon the fact that the ligands phenanthroline and 8-hydroxyquinoline have characteristics of big rigid planar, large absorption coefficient, and strong coordination. The luminescence emission spectra and the low temperature phosphorescence spectra of the two ligands were studied, and the experimental results showed that they have a strong tendency of energy transfer to the rare earth ion, and that the triplet state energies of Aphen and Hamq were 20000 and 22370 cm-1, respectively, which are much higher in energy than the resonance levels of Eu3+(5D0, 17200 cm-1), indicating that the triplet state energies of the two ligand are suitable for the sensitization of the luminescence of Eu3+, especially Aphen.2) The photophysical properties (color purity, luminescence intensity, lifetime, and quantum yield) of a series Eu(β-diketone)3(Aphen) complexes, complex Eu(TTA)2(amq), Eu(TTA)3(H2O)2 and Eu(TTA)2(AA) were investigated. The results showed that the complex Eu(TTA)3(Aphen) has the strongest luminescence emission among the series Eu(β-diketone)3(Aphen) complexes, and its luminescence intensity of 5D0→7F2 transition is 4.5, 11.3, and 3.9 times as high as that of Eu(TTA)3(H2O)2,Eu(TTA)2(AA) and Eu(TTA)2(amq), respectively, indicating that the acrylic acid ligand plays little or no role in the luminescence of Eu(TTA)2(AA) and the coordinated water molecules can effectively quench the luminescence intensity of Eu(TTA)3(H2O)2, and that the ligands Aphen and Hamq can sensitize the luminescence of Eu(Ⅲ) ion efficiently.3) Highly luminescent bonding-type Eu-containing copolymers were synthesized through the copolymerization of Eu(TTA)3(Aphen) or Eu(TTA)2(amq) with MMA, and characterized by FT-IR, UV-Vis,1H NMR, GPC, TGA, DSC, lifetime, and luminescence excitation and emission spectra. The results indicated that the Eu-complex moieties are directly bonded to the polymer backbone as an integrated unit, and the dissociation of the complex unit is negligible during the copolymerization and purification processes, that the thermal stabilities and the glass transition temperatures of the copolymers are enhanced upon the introduction of the Eu-complex moiety into the polymer chain, that the energy transfer is still mainly from the coordinated TTA although the MMA unit has taken part in the coordination, and that the copolymers all display the characteristic emissions of Eu(III) ions and five narrow emission peaks centered at 579,591, 612,651 and 698 nm, assigned to the 5D0→7F0,5D0→7F1,5D0→7F2,5D0→7F3,5D0→7F4 transitions, respectively, are well resolved, and the hypersensitive 5Do→7F2 transition is very intense. The luminescence intensities of the copolymers increased with an increase in the Eu content, and no significant concentration quenching phenomenon was observed at the Eu content within the studied range. The improvement of the luminescence properties for the copolymers may be attributed to the special microenvironment. On the one hand, the coordination stability of the Eu-complex unit in the copolymer is improved because the coordination degree of the unsaturated Eu-complex unit is satisfied through the intra- and intermolecular coordination, which results in the decrease of nonradiative decay rate of the excited levels of Eu(III) ion and the increase of the luminescence lifetime. On the other hand, the Eu-complex units can be twisted or distorted by the surrounding polymer chain, as the rare earth ions are kept in cages in the same polymer, resulting in so-called "cage effect". This may further lower the symmetry of the Eu(III) ion and consequently enhance the 5D0→7F2 transition of Eu-copolymers.4) In the Eu(TTA)2(amq)/PMMA blend system, the luminescence intensity increases with the increase in the Eu content and reaches a maximum at 3.30 wt% and then exhibits typical emission concentration quenching on further increase in the Eu content.