Development of models for predicting the properties of switchable mechanically interlocked molecular architectures

Mechanically interlocked molecular architectures (MIMAs) are supramolecular assemblies that are made up of non-bonded (mechanically linked) molecular components. Switchable rotaxanes and catenanes are a subclass of MIMAs with the unique property that they can switch their favored co-conformation (collective conformation of all non-bonded molecular units within the MIMA) in response to an external stimulus. These environmentally responsive systems are of interest because their switchable nature makes them promising candidates for the building blocks of nanoscale devices. The efficient development of nanoscale devices hinges on 'iterative design engineering', a process that involves using modeling to fine-tune the properties of switchable MIMAs for tailored applications by 'testing' the effects of proposed modifications without recourse to synthesis and fabrication. Theoretical methods play this role of testing the proposed design modifications and are therefore essential for developing and refining MIMA-based devices. Presented in this thesis are novel theoretical approaches for modeling the mechanical and charge transport properties of switchable rotaxanes and catenanes. Four approaches are reported: 1) prediction of the force generated by a rotaxane molecular muscle by means of semi-empirical electronic structure calculations, 2) development of a simulation tool to investigate the kinetics and net unidirectional motion of a catenane molecular motor, 3) characterization of the timescales of proton and electron transit in molecular systems in terms of statistical confidence by analyzing the time evolution of a particle's non-stationary wavefunction, 4) investigation of electron transit in the co-conformations of a rotaxane molecular switch by analyzing the time evolution of the system's non-stationary multi-electron wavefunction. These theoretical approaches produce results that are in agreement with experiment for the systems considered, and may serve as design tools for nanoscale devices based on switchable rotaxanes and catenanes.