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

An 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, N 2 adsorption, thermogravimetric analysis, FTIR and Raman spectroscopy, and 13 C and 29 Si CP MAS NMR spectroscopy. Pyridyl‐functionalised MCM‐41 (L″) was treated with chloroform solutions of lanthanide tris‐β‐diketonate complexes Ln(nta) 3 (H 2 O) 2 [Ln = Eu, Gd; nta = 1‐(2‐naphthoyl)‐3,3,3‐trifluoroacetonate] to give the surface‐bound monosubstituted species Ln(nta) 3 (H 2 O)(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 Eu 3+ red lines ascribed to transitions between the 5 D 0 excited state and the ground multiplet ( 7 F 0–4 ), and only very weak or negligible emission from the organic ligands are observed. Variation of the excitation wavelength confirmed that all of the Eu 3+ 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; Eu 3+ sensitisation occurs exclusively through the ligands rather than by direct intra‐4f 6 excitation.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)