Nanovalves

This article features both molecular and supramolecular chemistry involving: i) stimuli‐induced nanoscale movements within mechanically interlocked molecules; ii) the fabrication of mesoporous silica substrates; and iii) the integration of the mechanically interlocked molecular/supramolecular actuators to act as gatekeepers at the entrances to the silica nanopores into which guest dye molecules can be uploaded and released on demand from the mesoporous silica substrates. The supramolecular actuators are based on two [2]pseudorotaxanes—that is, 1:1 complexes that can be dissociated by external inputs, such as acid/base cycles, electrons, and light. The molecular actuators are based on bistable [2]rotaxanes and can be operated mechanically by using either redox chemistry or electrochemistry. After these pseudorotaxanes and bistable rotaxanes have been attached covalently to the orifices of the silica nanopores, stimuli‐controlled mechanical movements within these mechanically interlocked molecules can be harnessed to close and open the nanopores. Therefore, these mechanically interlocked molecules have been employed as nanovalves for controlled sequestering and release of guest dye molecules into and out of the mesoporous silica substrates. These actuators can be regarded as the prototypes of highly controllable drug‐delivery systems. Interlocked molecular and supramolecular actuators based on rotaxanes can act as gatekeepers at the entrances to nanopores in silica, into which guest dye molecules can be uploaded and then released on demand. Such actuators, or nanovalves (shown in the figure), can be operated using a wide range of stimuli, and can be regarded as the prototypes of highly controllable drug‐delivery systems.