MCM‐41 Derivatised with Pyridyl Groups and Its Use as a Support for Luminescent Europium(III) Complexes

Abstract

AbstractAn organic–inorganic hybrid ligand silica was prepared by reaction of the ordered mesoporous silica MCM‐41 with 3‐triethoxysilylpropyl 4‐pyridylacetamide. Elemental analysis indicated that a pyridyl group loading of 0.93 mmol g–1 was achieved. The derivatised material was further characterised by powder X‐ray diffraction, N2 adsorption, thermogravimetric analysis, FTIR and Raman spectroscopy, and 13C and 29Si CP MAS NMR spectroscopy. Pyridyl‐functionalised MCM‐41 (L″) was treated with chloroform solutions of lanthanide tris‐β‐diketonate complexes Ln(nta)3(H2O)2 [Ln = Eu, Gd; nta = 1‐(2‐naphthoyl)‐3,3,3‐trifluoroacetonate] to give the surface‐bound monosubstituted species Ln(nta)3(H2O)(L″). The residual coordinated water molecules were subsequently replaced by pyridine (py) or methyl phenyl sulfoxide (mpso) to give immobilised Ln(nta)3(py)(L″) and Ln(nta)3(mpso)(L″) species. Photoluminescence studies were carried out at room temperature and 14 K. The emission spectra of the Eu‐modified materials were dominated by the typical Eu3+ red lines ascribed to transitions between the 5D0 excited state and the ground multiplet (7F0–4), and only very weak or negligible emission from the organic ligands are observed. Variation of the excitation wavelength confirmed that all of the Eu3+ ions occupied the same average local environment within each sample. By comparison with the photoluminescence data for the nonsupported Eu(nta)3(py)2 and Eu(nta)3(mpso)2 complexes, it is shown that the interaction between the host and guest has a strong effect on the excited states of the organic ligands; Eu3+ sensitisation occurs exclusively through the ligands rather than by direct intra‐4f6 excitation.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)