Covalent attachment of 4-amino-1,8-naphthalimides onto the walls of mesoporous molecular sieves MCM-41 and SBA-15 Fabiane de Jesus Trindade, José Fernando Queiruga Rey, Sergio Brochsztain * Petroleum Nanotechnology Group, Universidade Federal do ABC, Rua Santa Adélia,166, Santo André-SP, 09210-170, Brazil article info Article history: Received 10 July 2010 Received in revised form 17 September 2010 Accepted 18 September 2010 Available online 29 September 2010 Keywords: 4-Amino-1,8-naphthalimides Solid state fluorescence Mesoporous materials MCM-41 SBA-15 Inclusion complexes abstract This work describes the covalent grafting of 4-amino-1,8-naphthalimides, which are fluorescent dyes with very interesting optical properties, onto the walls of mesoporous molecular sieves. The mesoporous materials MCM-41 and SBA-15 were first treated with 3-aminopropyltriethoxysilane, generating amine- rich surfaces that were further reacted with 4-amino-1,8-naphthalic anhydride, resulting in yellow fluorescent solids. The success of the modification reactions was confirmed by elemental analysis, X-ray diffraction patterns, infrared spectroscopy, scanning electron microscopy and UV/visible and fluores- cence spectroscopy. The emission spectra of the dye bound to MCM-41 was quite insensitive to solvent polarity, in contrast to dye-grafted SBA-15, which showed a high solvent sensitivity. These results suggest a tight fit of the dye molecules within the channels of MCM-41, leaving no room for the solvent mole- cules. In the case of SBA-15, the large pore size allows the invasion of the channels by solvent molecules, resulting in solvation of the encaged chromophore. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Mesoporous molecular sieves are nanostructured materials obtained by surfactant-templated synthesis, resulting in highly ordered hexagonal arrays of one-dimensional, three-dimensional or wormlike channels, with large surface area and narrow pore size distribution [1,2]. Among the most well-known mesoporous molecular sieves are the MCM-41 [1] and SBA-15 [2] families, with pore sizes in the range 2e10 nm and 5e30 nm, respectively. Initially, researchers were interested in these materials as catalysts for the petroleum industry [3,4], in substitution for the zeolites. More recently, however, with the development of nanotechnology, it was acknowledged that these nanostructured materials have a great potential for novel applications in photonics and electronics, since they can incorporate large organic dyes [5,6]. Examples of organic dyes that have been incorporated into mesoporous silicates are porphyrins [7], phthalocyanines [8,9], methylene blue [10] and ferrocene [11]. The incorporation of fluorescent dyes is particularly interesting for the construction of optical devices, such as nano- lasers and fluorescent nanoparticles for medical diagnosis [12e15], since the organized mesoporous framework usually prevents dye aggregation, increasing the fluorescence. Most studies on the incorporation of fluorescent dyes into mesoporous molecular sieves, however, have been restricted to rhodamine, fluorescein and coumarin derivatives [5,6,12e15]. Our group [16,17] and others [18] have recently reported on the incorporation of a different class of dyes, the 3,4,9,10-perylenediimides (PDI), into the channels of mesoporous materials MCM-41 and SBA-15. In a continuation to our efforts towards preparing new materials based on fluorescent aromatic imides, we report herein on the covalent grafting of 4-amino-1,8-naphthalimides (ANI) in the pores of MCM-41 and SBA-15. A recently published article described the encapsulation of a ANI derivative within the pores of MCM-41 [19], but in that case the dye was incorporated by sorption, and not by covalent bonding. The 4-amino-1,8-naphthalimides (ANI) constitute a class of strongly fluorescent yellow dyes with very interesting photo- physical properties [20e23]. Thank to these properties, the ANI have been used in several applications, ranging from electrolumi- nescent devices [24] to sensors for cations and anions [25e29], molecular switchers [30,31], artificial photosynthetic systems [32e34] and thermochromic [35] and pH sensing [36] devices. The ANI are also useful as building blocks for the construction of supramolecular systems, such as rotaxanes, catenanes [37] and inclusion complexes with cyclodextrins [38,39]. In order to bind covalently the ANI chromophore to MCM- 41 and SBA-15, we first modified the pore walls with 3- * Corresponding author. Tel./fax: þ55 11 49963166. E-mail address: sergio.brochsztain@ufabc.edu.br (S. Brochsztain). Contents lists available at ScienceDirect Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig 0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2010.09.009 Dyes and Pigments 89 (2011) 97e104