Light-Activated Polymer-Coated Mesoporous Silica with Azobenzene Moiety for the Controlled Delivery of Guest Molecules

In this study, we have synthesized a light-activated polymer-coated mesoporous silica nanovalve with poly(trans-4-methacryloyloxyazobenzene-co-methylmethacrylic acid-co-vinyltrimethoxysilane) (PMMV) (MSNs/PMMV) for the controlled delivery of guest molecules. The hydrophobicity of azobenzene varies depending on the structure of each isomer. Typically, trans isomers are hydrophobic due to the aromatic ring, but they become more hydrophilic when they are changed to the cis confirmation. Using this concept, we introduced PMMV as a light active nanovalve on the mesoporous silica. To optimize the coating of the light-activated polymer on mesoporous silica, we investigated the conformational change of PMMV in solutions at various pHs. PMMV has a dot-like morphology in acidic solutions under pH 4, but sheet-like morphology in solutions at pH over 4. We investigated the nanovalve behavior of MSNs/PMMV by introducing propidium iodide (PI) as guest molecules. Time-resolved fluorescence spectroscopy showed the excellent light activity of PMMV for open pores. The new PMMV-coated mesoporous silica could be applied in the smart nanovalve system for the controlled delivery of various guest molecules.