Photo-driven expulsion of molecules from mesostructured silica nanoparticles

Azobenzene derivatives act as both impellers and gatekeepers when they are tethered in and on mesoporous silica nanoparticles. Continuous excitation at 457 nm, a wavelength where both the cis and trans conformers absorb, produces constant isomerization reactions and results in continual dynamic wagging of the untethered terminus. The 2 nm diameter pores are loaded with luminescent probe molecules, azobenzene motion is stimulated by light, and the photoinduced expulsion of the probe from the particles that is caused by the motion is monitored by luminescence spectroscopy. The light-responsive nature of these materials enables them to be externally controlled such that the expulsion of dye molecules from the mesopores can be started and stopped at will. These results open the possibilities of trapping useful molecules such as drugs and releasing them on demand.