Persuading molecules to behave in a responsible manner

September/October 2015

Electronic design is butting up against the physical limits of manipulating charges within a semiconductor, which means circuitry is approaching the effective limit of how small and densely packed it can become. However, that density could be increased by many orders of magnitude if you can persuade molecules to behave as the switches responsible for storing or manipulating information.

Molecular “shuttling” is made possible by metal-organic framework­ materials in the form of a linked axle, strut and wheel, which make it possible for the resulting structure­ to move between two distinct positions.

Molecular “shuttling” is made possible by metal-organic framework­ materials in the form of a linked axle, strut and wheel, which make it possible for the resulting structure­ to move between two distinct positions. Photo credit: Stephen Loeb

Researchers at the University of Windsor’s Department of Chemistry and Biochemistry have done just that, demonstrating how interlocked metal-organic molecular frameworks can be formed in a wheel-and-axle arrangement that moves back and forth in a consistent, repeatable fashion that could serve as the “on” and “off” positions that lie at the heart of binary logic. 

Stephen Loeb, FCIC, one of the professors in the department, traces the roots of this work to pioneering research on interlocked molecular assemblies that appeared in the early 1990s. These initial observations took place in solution, which made them interesting but not practical for potential microelectronic applications. More recently Loeb and his colleagues had created metal-organic frameworks (MOFs) that rotated predictably in the solid-state. Now they have been able to show these frameworks will support the large amplitude, translational motion known as “shuttling” in a solid-state setting, a result that was just published in Nature Chemistry. “It’s taken the better part of 25 years to get to the point where we could put them in a condensed phase and make them highly dense and organized,” Loeb says, noting these mechanically interlocked molecules move about a nanometre some 300 times a second. That rate might seem slow compared to the blazing speed of contemporary data processing but if such activity were multiplied and scaled up, it could represent a fundamentally new strategy for building electronic systems.

Before that can happen, however, Loeb points out that the next step is determining how this motion can be controlled by electrical or optical perturbation. “That would be a true switch,” he says, “and we’re working on that now.”