Luminescence for Grafting Organic Molecules on γ-Alumina via the Reaction of Alumina and Organic Compounds

Abstract

Scheme 1. Reaction of organic molecules with γ-alumina under microwave irradiation or reflux. The grafting of organic moieties onto the surface of inorganic compounds is an important in numerous applications such as organic synthesis on solid phases and the modification of the surface properties of solids. Alumina is one of the most interesting inorganic materials for grafting organic moieties. Alumina has pore structure for ease diffusion of organic compounds and excellent properties as high melting point, low electrical conductivity, thermal and chemical stability and oxidation and corrosion resistance. However there are not many reports on preparing methods and optical properties of organic-alumina hybrid materials. Here we report the preparation of hybrid material grafting organic moieties on alumina and investigation of their photoluminescence (PL) properties. Although several reactions of phosphoric or phosphonic derivatives with alumina have been reported, the other organic functional groups do not have been used for grafting organic moieties on alumina. We have prepared the hybrid materials which used to graft organic moieties on alumina through the microwave irradiation or reflux, and investigated their PL properties. To prepare the hybrid materials with organic moieties on alumina, the readily available commercial γ-alumina 2 (surface area is 132 m/g) is used, and benzoyl chloride (1a), hexanoyl chloride (1b), heptyl bromide (1c), naphthoic acid (1d) were used as organic compounds. Benzoylalumina hybrid material 3aM was prepared from the reaction of benzoyl chloride (1a) and γ-alumina 2 without solvent in microwave irradiation for 15 minutes. On the other hand, benzoylalumina hybrid material 3aR was prepared in the reflux condition for 12 hours. After cooling to room temperature, the crude products were washed with dichloromethane (3 × 50 mL), ethylacetate (3 × 50 mL), hexane (3 × 50 mL), and methanol (3 × 50 mL). Hexanoylalumina 3bM, 3bR and heptylalumina 3cM, 3cR were prepared using hexanoyl chloride (1b) and heptyl bromide (1c) with γ-alumina 2 on microwave irradiation or reflux conditions. The toluene solution of naphthoic acid (1d) and γalumina 2 was irradiated by microwave at 150 W for 15 minutes and same solution was refluxed for 12 hours to get naphthoicalumina 3dM and 3dR. Each washed material, 3aM, 3aR, 3bM, 3bR, 3cM, 3cR, 3dM, 3dR was dried in vacuum as well as in oven, each for 24 hours to remove the organic solvent in porous site (Scheme 1) and (Table 1). Each organic grafting alumina was characterized by elemental analysis and IR. Graft densities (δ) of the covalently attached organic molecules (1a-d) in γ-alumina 2 were determined by carbon elemental analysis (eq 1), where gE is the C content, ME is the molecular weight of C, Z is the number of C atoms per organic group.