Controlling the Density of Amine Sites on Silica Surfaces Using Benzyl Spacers

The synthesis and characterization of benzyl-spaced aminopropyl-functionalized mesoporous silica is reported by a method designed to reduce silanol-amine and amine-amine interactions. The new material is characterized by N(2) physisorption, thermogravimetric analysis, potentiometric titration, X-ray diffraction, FT-Raman spectroscopy, and (13)C and (29)Si solid-state NMR spectroscopy. The degree of clustering of the amines is studied by solid-state fluorescence spectroscopy of 1-pyrenecarboxylic acid bound to the deprotected benzyl-spaced aminosilica. The results obtained provide evidence of an amine loading comparable to traditional dense amine grafting approaches on SBA-15. Thermogravimetric analysis, FT-Raman spectroscopy, and (13)C solid-state NMR spectroscopy results show evidence that the protected imine can be quantitatively cleaved to yield the corresponding amine. As evidenced by fluorescence spectroscopy, the benzyl-spaced material is isolated enough to prevent excimer formation of the probe molecule, unlike aminopropyl-functionalized silica materials prepared by traditional grafting approaches.