Computational Investigation of the Role of Counterions and Reorganization Energy in a Switchable Bistable [2]Rotaxane

Abstract

Switchable bistable [2]rotaxanes, such as those of the Stoddart-Heath-type, show promise for the development of molecular electronic devices and functional prototypes have been demonstrated. Herein, one such switchable rotaxane system is studied computationally at the AM1-FS1 and DFT levels of theory. The results show that the computationally efficient AM1-FS1 method, (efficient relative to DFT) is capable of reliably predicting properties such as binding site preference and coconformational relative stabilities as well as the barrier to isomerization between the different coconformational states. These properties play important roles in the functionality of rotaxane-based molecular electronic devices. In addition, the role of the counterions is assessed from a computational standpoint. The results reveal that inclusion of counterions is not as significant as has been previously suggested. Finally, the reorganization energy associated with oxidation/reduction of the complex is studied. This provides a possible link to the origin of the observed conductivity difference between the two coconformational states, the property upon which device functionality is based.