Molecular Construction and Photophysical Properties of Luminescent Covalently Bonded Lanthanide Hybrid Materials Obtained by Grafting Organic Ligands Containing 1,2,4-Triazole on Silica by Mercapto Modification

This study focuses on the syntheses of a series of organic−inorganic hybrid materials in which the triazole heterocyclic organic components were grafted into the silica backbone via covalent bonds through a sol-gel process. The organic parts 3-alkyl-4-amino-5-ylsulfanyl-1,2,4-triazole (O1 and O2) were first prepared by the reaction of thiocarbohydrazide with acetic acid or propionic acid, respectively, and then functionalized with trialkoxysilyl groups, and the as-obtained silylated monomers (P1−P4) were used as the siloxane network precursors to coordinate to Eu 3+ or Tb 3+ and further introduced into silica matrixes by Si−O bonds after hydrolysis and polycondensation processes. The preparation of the hybrid materials (LnM1−LnM4, Ln = Eu and Tb) including covalent grafting is described, as well as their structures and the photophysical properties. All of the materials are totally amorphous and no phase separation happened. The spectroscopic date revealed that all these hybrids can show the characteristic luminescence of Eu 3+ or Tb 3+ ions for the energy transfer process takes place successfully between the organic parts and the RE ions. Modifications by different trialkoxysilyl groups (3-(triethoxysilyl)propyl isocyanate or 3-chloropropyl trimethoxysilane) lead to the different coordination structures and thus influence the absorption efficiency or the ability of the organic ligands to transfer the absorbed energy to Ln 3+ ions and consequently changed the luminescence lifetimes and the quantum yield of the emission.