Free Energy Barrier for Molecular Motions in Bistable [2]Rotaxane Molecular Electronic Devices
Abstract
Donor-acceptor binding of the electron-poor cyclophane cyclobis with the electron-rich tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) stations provides the basis for electrochemically switchable, bistable [2]rotaxanes, which have been incorporated and operated within solid-state devices to form ultradense memory circuits and nanoelectromechanical systems. The rate of CBPQT4+ shuttling at each oxidation state of the [2]rotaxane dictates critical write-and-retention time parameters within the devices, which can be tuned through chemical synthesis. To validate how well computational chemistry methods can estimate these rates for use in designing new devices, we used molecular dynamics simulations to calculate the free energy barrier for the shuttling of the CBPQT4+ ring between the TTF and the DNP. The approach used here was to calculate the potential of mean force along the switching pathway, from which we calculated free energy barriers. These calculations find a turn-on time after the rotaxane is doubly oxidized of 10-7 s (suggesting that the much longer experimental turn-on time is determined by the time scale of oxidization). The return barrier from the DNP to the TTF leads to a predicted lifetime of 2.1 s, which is compatible with experiments.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 10, 2009
- Accession Number
- ADA507037
Entities
People
- Fraser Stoddart
- Hyungjun Kim
- James R. Heath
- Seung S. Jang
- William Andrew Goddard III
- William Dichtel
Organizations
- California Institute of Technology