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Keywords:

  • Luminescence;
  • Mesostructured materials;
  • Ruthenium complexes;
  • Sensors, gas;
  • Silica;
  • Sol–gel processes

Abstract

Novel oxygen sensors consisting of a [Ru(bpy)2phen]2+ (bpy: 2,2′-bipyridyl, phen: phenathroline) portion covalently grafted to a mesostructured silica-based network are prepared in situ via a sol–gel approach with the help of cetyltrimethylammoniumbromide (CTAB) surfactant. 1,10-Phenanthroline covalently grafted to 3-(triethoxysilyl)propyl isocyanate is used as not only the sol–gel precursor but also as the second ligand of the Ru(bpy)2Cl2 · 2H2O complex to prepare the sol–gel-derived mesostructured silicates for an oxygen sensor. For comparison purposes, the oxygen sensors in which [Ru(bpy)2phen]Cl2 is conventionally physically incorporated into the matrix are also prepared. Elemental analysis, NMR, Fourier transform IR, UV-vis electronic absorption, luminescence-intensity quenching Stern–Volmer plots, and excited-state decay analysis are used to characterize the obtained oxygen sensors. These obtained bulk xerogels and spin-coated thin films show that the homogeneity and the sensitivity of the covalently grafted samples are superior to those of the physically incorporated ones, and the highest sensitivity is obtained in the mesostructured bulk xerogel. This improvement in oxygen sensitivity is attributed to the increased diffusivity of oxygen in the uniform and nearly parallel porous structure of the Mobil Catalytic Material 41 mesostructured matrix, the enhanced homogeneity results from the covalently grafted propyl group in –Si–(CH2)3– that acts as the fundamental spacer which prevents interaction between the attached RuII complex and the silica matrix, and optimal dispersion in the mesopores during the sol–gel polycondensation. Furthermore, the greatly minimized leaching effect of the sensing molecules could be observed in the covalently grafted system. The covalent grafting strategy presented in this paper provides superior optical oxygen sensors with homogeneous distribution, improved sensitivity, and simplified calibration plots.