Highly luminescent europium(III) complexes containing organosilyl 4,4,5,5,5-pentafluoro-1-(naphthalen-2-yl)pentane-1,3-dionate ligands grafted on silica nanoparticles† D. B. Ambili Raj, Silvanose Biju and M. L. P. Reddy * Received 10th July 2009, Accepted 20th August 2009 First published as an Advance Article on the web 14th September 2009 DOI: 10.1039/b913786f A novel organic–inorganic mesoporous luminescent hybrid material was designed by linking a ternary Eu 3+ complex to the functionalized hexagonal mesoporous MCM-41 with the modified b-diketone, 4,4,5,5,5-pentafluoro-1-(naphthalen-2-yl)pentane-1,3-dione (HPFNP), which contains a polyfluorinated alkyl group as well as the long conjugated naphthyl group. b-Diketone grafted to the coupling agent 3-(triethoxysilyl)propylisocyanate was used as the precursor for the preparation of mesoporous materials. MCM-41, consisting of ternary complex, Eu(PFNP-Si) 3 (bath) covalently bonded to the silica-based network, which was designated as Eu(PFNP-Si) 3 (bath)/MCM-41, was obtained by interacting europium nitrate, SiPFNP-Na and 4,7-diphenyl-1,10-phenanthroline (bath) into the mesoporous material via a ligand-exchange reaction. The synthesized luminescent hybrid material was fully characterized by various spectroscopic techniques, and its photophysical properties were investigated. Eu(PFNP-Si) 3 (bath)/MCM-41 exhibits an efficient intramolecular energy transfer process from the silylated b-diketone to the central Eu 3+ , namely, the ‘‘antenna effect’’, which favoured highly luminescent behaviour in the modified hexagonal mesoporus silica. Introduction Recently, lanthanide-containing inorganic–organic hybrid materials has attracted considerable attention due to their unique photophysical properties 1 and specific functions make them useful in a wide range of photonic applications that includes tunable lasers, 2 amplifiers for optical communications, 3 and components of emitting materials in multilayer organic light- emitting diodes. 4 It is well documented that organolanthanide complexes, especially with ligands b-diketones, 5 aromatic carboxylic acids, 6 and heterocyclic ligands 7 have characteristic luminescence properties and give sharp, intense emission lines upon ultraviolet light irradiation, because of the effective intra- molecular energy transfer from the coordinated ligands to the central Ln 3+ ions (the ‘‘antenna effect’’). 8 However, the poor stabilities and low mechanical strength of the lanthanide complexes always hinders their use in practical applications such as tunable solid-state lasers or phosphor devices. In order to overcome these shortcomings, many research efforts are focused on preparing lanthanide organic–inorganic hybrids through functionalization of the exterior and/or interior surfaces, prompting the utilization of mesoporous materials such as MCM-41 9–11 and SBA-15. 12,13 Conventional methods of doping lanthanide complexes into silica matrices seem unable to solve the problem of the quenching effect of luminescent centers because only weak interactions such as hydrogen bonding, van der Waals forces, or weak static effects 14,15 exist between organic and inorganic moieties. Furthermore, inhomogeneous dispersion of two phases and leaching of the photoactive molecules frequently occur in such designed hybrid materials for which the concentration of complexes is also greatly reduced. Due to the above reasons, another novel approach concerning the complexation of lanthanide ions using antenna chromophore ligands that are covalently bonded to the inorganic networks has emerged. Several reports are available on the covalent grafting of lanthanide b-diketone chelates to silica hosts. 1a,9–12,16–25 However, in most cases the co-ligands 1,10-phenanthroline 16,24 or 2,2 0 - bipyridyl 25 bridged covalently bonded hybrids and the b-dike- tones simply behave as second ligand to the Ln 3+ ion. On the other hand, recently a few investigations have described the modification of b-diketones and lanthanide chelates directly covalently bonded to the silica host, in which bidentate nitrogen donors bind to the central Ln 3+ ions to saturate the coordination sphere. 12,20,21 Novel organic–inorganic mesoporous luminescent hybrid materials were designed by linking the ternary Eu 3+ complexes to the functionalized ordered mesoporous SBA-15 with the modified 1-(2-naphthoyl)-3,3,3-trifluoroacetonate (NTA). 12 Further investigations on the luminescence properties of Eu-(NTA-SBA-15) 3 bpy mesoporous materials show that they exhibit characteristic luminescence of the corresponding Eu 3+ , through intramolecular energy transfer from the modified ligand (NTA-Si) to the central Eu 3+ ion, and higher 5 D 0 luminescence quantum efficiencies and longer lifetime than the pure Eu(NTA) 3 bpy complex. 12 However, the synthesis and Chemical Sciences and Technology Division, National Institute for Interdisciplinary Science & Technology (NIIST), CSIR, Thiruvananthapuram 695 019, India. E-mail: mlpreddy55@gmail.com † Electronic supplementary information (ESI) available: 1 H NMR spectra of SiPFNP-Na, Solid-state 29 Si NMR spectra of MCM-41, DLS particle size distribution curve, TEM pictures and Thermogravimetric curve for Eu(SiPFNP) 3 (bath)/MCM-41, and phosphorescence spectra of Gd(PFNP-Si) 3 (H 2 O) 2 and Gd(PFNP) 3 (H 2 O) 2 described in this manuscript. See DOI: 10.1039/b913786f 7976 | J. Mater. Chem., 2009, 19, 7976–7983 This journal is ª The Royal Society of Chemistry 2009 PAPER www.rsc.org/materials | Journal of Materials Chemistry