Adsorption of tris(8-hydroxyquinolinato)aluminum on phosphoric acid-containing mesoporous silica particles

Abstract

The effect of the phosphoric acid addition on the nanostructures of the mesoporous silica (MPS) particles and the states of tris(8-hydroxyquinolinato)aluminum (Alq3) in the mesopores were investigated. It was found that the regularity of the mesopores of the MPS particles became irregular by the excessive addition of phosphoric acid. Furthermore, the phosphoric acid on the silica skeletons in the mesopores would strictly interact with the Alq3 molecules, so that the proportion of monomer components with less overlap among the π-π orbitals (i.e., δ-phase-like Alq3 molecules) increased with increasing the phosphoric acid, which was effectively monitored in the fluorescence spectra. It was suggested that the interactions between Alq3 and mesopores were formed not only by hydrogen bonds but also by electrostatic forces between P–O− and aluminum ion, and then the Alq3 molecules were planarly fixed on the surfaces, indicating the importance of the phosphoric acid addition for fixing the photofunctional species on the mesopores.