Boehmite Supported Pyrene Polyamine Systems as Probes for Iodide Recognition Esther Carbonell,* ,† Estefanía Delgado-Pinar, † Javier Pitarch-Jarque, † Javier Alarcó n, ‡ and Enrique García-Españ a* ,† † Departament de Química Inorga ̀ nica, Universitat de Valè ncia, Institut de Cie ̀ ncia Molecular (ICMOL), 46980 Paterna, Vale ̀ ncia, Spain ‡ Departament de Química Inorga ́ nica, Universitat de Valè ncia, 46100 Burjassot, Vale ̀ ncia, Spain * S Supporting Information ABSTRACT: New organic−inorganic fluorescent probes made by attaching the tripodal polyamine (tris(2- aminoethyl))amine (tren), propylamine, or diethylenetriamine functionalized with pyrene as a fluorophore to an γ-aluminum oxohydroxide matrix have been prepared and studied both in solution and supported on the surface of boehmite nano- particles. Both kinds of systems have been revealed as sensitive and selective fluorescence turn-off chemosensors for iodide in aqueous solution with an estimated detection limit that reaches 36 ppb. The recognition characteristics and photophysical properties of these molecules are essentially preserved when they are grafted to the surface of the particles. Since the nanoparticles are stable over a wide pH window and they can be easily recovered by centrifugation and filtration, these systems present the advantage that can be repeatedly used for the detection of iodide. ■ INTRODUCTION The design and synthesis of chemosensors capable of recognizing anions have attracted much attention in recent years due to fundamental roles played by the anions in a wide range of biological, chemical, and environmental processes. 1−4 The anions have a variety of special features that must be addressed to prepare effective receptors. They generally have large size and variable shape, are strongly solvated, can only exist in specific media, and interact only through weak forces. The most effective way to bind anions consists of taking advantage of their negative charge. Accordingly, protonated polyamines have been the principal receptors of choice, since they ensure intense electrostatic attractions reinforced by hydrogen-bond contacts with the coordinated anions. 5−9 In order to signal the binding of the analyte to the receptor, we need a unit with a property that changes largely following the binding event. In this respect, fluorescent signaling units are very efficient because of the high sensitivity, rapid response, and simple instrumentation required for the measurement. 10 For this study, we have chosen pyrene as a fluorophore, since it presents high fluorescence quantum yield and long singlet lifetime. Therefore, pyrene has been widely used as a signaling unit for a variety of analytes including inorganic anions. 11−14 On the other hand, aiming to obtain more efficient, selective, and sensitive chemosensors, an increasing number of papers have recently appeared in which the chemosensor is anchored to different supports such as microporous and mesoporous materials, 15 silica nanoparticles, 16,17 gold nanoparticles, 18,19 quantum dots, 20 and boehmite nanoparticles. 21 In this regard, our group has been working in the use of boehmite nanoparticles as support in different fields. 21−26 The use of boehmite nanoparticles presents advantages such as the possibility to make fluorescence emission studies in pure water with little scattering, and the recovering of the sensor system after their use by centrifugation because a change from a sol to a gel state occurs at basic pH. Moreover, boehmite, which is an aluminum oxyhydroxide (AlO(OH)), contains terminal groups that render high reactivity to the surface and provide a hydrophilic environment improving the homogeneity of the medium being for all these reasons a promising support. In this context, we have prepared three new organic− inorganic covalently linked materials which contain pyrene as the fluorophore, the polyamine as the coordination site (receptor), and boehmite as the support. To analyze the role played by the support, we have also prepared the analogous unsupported ligands. The materials will be named as BTpy/ Tpy, B3Npy/3Npy, and B1Npy, where B stands for boehmite, 3N and 1N stand for the number of nitrogen atoms in the lineal chain, T corresponds to the tris(2-aminoethyl)amine tripodal structure, and py stands for pyrene. We have examined the photophysical properties and the photochemical response of the supported and unsupported materials in a wide pH range. Finally, we have studied the interaction of both types of systems with fluoride, chloride, bromide, iodide, sulfate, and phosphate anions. Received: April 2, 2013 Revised: June 12, 2013 Published: June 17, 2013 Article pubs.acs.org/JPCC © 2013 American Chemical Society 14325 dx.doi.org/10.1021/jp4032546 | J. Phys. Chem. C 2013, 117, 14325−14331