Lantanoid(III) ions sensitized by crown ethers as precursors of bimetallic luminescent heteroleptic complexes with block metals d: synthesis, characterization and evaluation of optical properties

Abstract

Lanthanoids(III) display well-defined IR to UV-Visible emissions mainly from transitions involving f orbitals, which are prohibited by Laporte's Rule, and dependent on the nature of each metal, but exhibiting a relative low molar absorptivity due to the mentioned selection rule. Thus, it is common to use the coordination of organic ligands to these metals in order to sensitize the central ion by metal complexes formation, enabling the energy transfer ligand-metal and enhancing the emission efficiency, the so-called "antenna effect". This energy transfer occurs after an intersystem crossing (ISC) between an excited singlet to an excited triplet states of the molecule, which is prohibited by the spin selection rule. In addition, transition metals such as Re, Os, Ru, Cr, or Ni can be coordinated to the organic molecule and thus facilitate ISC by relaxing the selection rules induced by strong spin-orbital coupling, increasing ISC rates. Therefore, compounds containing lanthanoid coordinated to a complex of a transition metal aim to amplify the antenna effect. The goal of this project is to synthesize and evaluate systems containing the crown ether ligand class, aiming the sensitizing action of them, in the formation of luminescent complexes with Eu3+ ions, for red emission, and Er3+, for infrared ones, under excitation in the UV-Vis. The investigation of the occurrence or not of upconversion processes in the case of the Er3+ complexes will be done as well. Lanthanum(III) analogous complexes will also be prepared for the determination of the ligands triplet state and to enable the NMR spectra acquisition. It is also intended the development of binuclear systems, where the ligand that will bind the metal centers will be 2,2-bipyrimidine, which will have the function of replacing any water molecule coordinated to the lanthanoid in the crown ether precursor complex, and to act as a bridge to coordinate with the complex of the block metal d. In this case, the selected metals are Cr3+ and Ni2+, where it will be studied and compared the action of these ions in the luminescence process of the final hetero-binuclear system in relation to the complexes based only on lanthanoids and crown ether. (AU)