Photoresponsive Mesoporous Materials

In 1992, Kresge and coworkers at Mobil invented the so-called MCM-41 mesoporous materials that have a hexagonal arrangement of monosized mesopores with pore size adjustable from 1.5 nm to 10 nm (Kresge et al., 1992). 

Two synthetic methods have been exploited to incorporate azobenzene moieties into mesoporous silica frameworks. The postgrafting method involves functionalizing mesoporous sol-gel materials with reactive azobenzene derivatives to tether azobenzene moieties to sol-gel matrices. The one-pot synthesis method requires 

Brinker and coworkers also prepared photoresponsive nanoporous silica particles using aerosol-assisted assembly, EISA, and surfactant-directed self-assembly (SDSA) techniques (Liu, 2004). The as-prepared photoresponsive nanocomposite particles were prepared so that the azobenzene ligands pointed toward the hydrophobic micellar interiors. After surfactant removal by solvent extraction, nanoporous particles with azobenzene ligands positioned on the pore surfaces were formed (Fig. 13.8). 

Pore size and Distribution. Nitrogen sorption isotherms were widely used to estimate the pore size and distribution of mesoporous materials. 

The azobenzene ligands incorporated into the mesoporous silica materials undergo photoisomerization upon light irradiation. Compared with the photoisomerization of the azobenzene ligands in solution, it exhibited some difference as described later. 

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This chapter focuses on azobenzene-containing organosilanes that are precursors for preparing photoresponsive silica materials, mesoporous sihca materials with azobenzene moieties on the pore surfaces, and azobenzene-modified polysilsesquioxane gels. 

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