Tiny Molecular-Scale Devices May Lead To Faster Computers

The devices -- including a five-molecule-long wire that measures just 9-billionths of a meter end to end -- could help engineers make computer circuits up to 100 times smaller than current sizes. That's important, because the smaller the circuitry, the faster the computer.

"We're taking information processing into the molecular realm," says lead researcher Dr. Jonathan Lindsey, Glaxo Distinguished University Professor of Chemistry at NC State. "Now that we've made the wire and figured out how it works and how to make it better, we can apply that knowledge to building logic gates, input-output elements, and other molecular-scale materials for computer circuits."

The pioneering work of Lindsey's team has put them at the forefront of an emerging new scientific field called molecular photonics. They will present an overview of their work, along with recent discoveries about factors that affect the flow of energy through their wire, in 10 presentations at the American Chemical Society's 1999 national meeting, March 21-26 in Anaheim, Calif.

Unlike conventional circuitry, the wire that's been built by Lindsey and his colleagues doesn't conduct electricity, nor is it an optical fiber. Rather, it's a series of pigments, similar to chlorophyll, that works on a principle similar to photosynthesis, the process by which plants' leaves absorb light and convert it into stored energy. Lindsey's wire works by absorbing blue-green light on one end and electronically transmitting it as light energy to the other end, where a fluorescent dye emits the signal as red light.

Although this process may seem novel to laymen, "scientists have long known that electronic communication occurs in molecules, such as in the flow of light energy from one chlorophyll molecule to another in photosynthesis," Lindsey says.

"Our research looks at ways to control this energy flow and use it to create future generations of super-fast, molecular-scale computer circuitry and information processing devices," he says. They also are working to build molecular photonic devices for use in solar-energy systems.

The idea behind the molecular photonic wire first came to Lindsey 17 years ago while he was in graduate school -- a time when methods for working on such minuscule devices didn't exist. But by 1994, the technology was in place to allow Lindsey, then at Carnegie Mellon University, to build a five-molecule-long prototype that acted as a passive carrier of electronic signals.

At the American Chemical Society meeting this month, he and his team will show how far the research has come.

One of their biggest advances has been learning how to increase the speed of energy flow along the wire. Previously, Lindsey explains, it was thought that energy flow was controlled by four factors: distance between molecules; molecules' orientation; their energies; and their environment. But the rate of energy flow observed in seemingly similar molecules was sometimes dramatically different. What could be causing this, researchers wondered, and how could it be controlled?

Two postdoctoral fellows in Lindsey's lab, Drs. Thiagarajan Balasubramanian and Jon-Paul Strachan, found the answer. They proved that a fifth factor, the orbital -- the pattern in which electrons are distributed within a molecule -- also affects the energy flow. Balasubramanian and Strachan found that if linkers joining the molecules are positioned at sites with high densities of electrons, energy flow is faster and more efficient.

"Sites with high electron densities are like spigots from which energy is ready to flow," Lindsey says. "Knowing this opens a lot of doors in designing new materials."

"As engineers approach the practical limits of shrinking circuitry size by the conventional method of cutting bulk materials into smaller pieces, it's only a matter of a few decades before the dimensions of computer circuitry enter the molecular scale," he says.

In addition to Balasubramanian and Strachan, Lindsey's chief collaborators are Dr. David Bocian, a former NC State student who is now professor of chemistry at the University of California at Riverside; and Dr. Dewey Holten, professor of chemistry at Washington University in St. Louis.

Principal research funding comes from the National Science Foundation. The U.S. Department of Energy also sponsors Lindsey's work on potential uses for molecular photonic wires in solar-energy technologies.