Covalent attachment of 4-amino-1,8-naphthalimides onto the walls of mesoporous molecular sieves MCM-41 and SBA-15

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 fluorescence 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 molecules. 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.