| The success of future molecule-driven actuators most likely lies in the development of artificial molecular motors because of their ability to provide large forces from low voltage inputs while also featuring bistable actuation characteristics and molecular design flexibility. With these advantages in mind, we are interested in developing mechanical devices using the force and movement generated by the molecular switching process of artificial molecular motors---rotaxanes---as a power source and actuator. Before any rotaxane-based mechanical devices become viable for realistic applications, however, mechanical switching behavior must be proven indisputably while the molecules are mounted on solid supports. Here, we demonstrate, for the first time, that amphiphilic, bistable rotaxanes all mechanically switchable in closely-packed Langmuir films, and verify quantitatively the movement of the ring component from one station to the other by X-ray photoelectron spectroscopy (XPS). The same mechanical motion has also been observed when these particular motor-molecules are mounted on a solid support as Langmuir-Blodgett (LB) films. We further developed an in situ Fourier-transform infrared (FTIR) spectroscopic technique to monitor molecular behavior in single-molecule thick crossbar junction devices. This approach is applicable to a range of molecular-based devices and has the potential to provide researchers in the field of molecular mechanics and molecular electronics with a tool to understand the molecular behavior that contributes to device performance. Finally, we developed the first rotaxane-based nanomechanical device utilizing a hybrid top-down bottom-up fabrication approach. An array of microcantilever beams, coated with a self-assembled monolayer of a palindromic [3]rotaxane "molecular muscle," undergoes controllable and reversible bending as chemical oxidants and reductants are injected into the fluid cell. Control experiments and theoretical analysis suggest that the bending of the beams occurs in direct response to the surface stress caused by the redox-activated nanomechanical motion of the [3]rotaxane. By transducing chemical energy into mechanical work, this system provides a key component for the development of nanoelectromechanical systems (NEMS). |
