UO chemists closer to making organic molecules for electronics

Stock image shows old data storage devices

With a couple of chemical tweaks, University of Oregon chemists have taken a step forward in efforts to harness organic molecules as a cheaper alternative to traditional silicon-based conductors in digital storage devices.

The research, done primarily in Michael Haley’s UO lab, is part of a worldwide effort by scientists in the last two decades to tap potential electronic properties of a class of carbon-based structures that were first synthesized more than a century ago. Overcoming the instability of the molecules has been a long-running challenge in making them capable of performing as well as silicon-based, or inorganic, electronics.

In the project, a 10-member team, led by UO doctoral student Justin Dressler and former visiting Japanese scientist Mitsuru Teraoka, used sulfur-rich thiophene and benzene building blocks in their synthesis of one of the molecules. The result, published last month in the journal Nature Chemistry, exceeded the team’s expectations.

“Including these pieces completely changed the properties of these molecules,” Dressler said. “Our compounds went from having all double bonds to having two radical centers and eliminating one of the double bonds. Organic molecules that possess this diradical character are very rare and not well understood.”

Translated, the team created an open-shell molecule in which they could control how electrons spin at varying temperatures, an important step for efficiency of data transfer and storage. In what is known as a singlet, or zero, state, electrons spin in opposite directions. The new work unveiled a way to control the flipping of spin to make it go parallel, providing a triplet state where the bonding enters the 1 state.

“We have begun to learn how to dial in the temperature by rational modification of the molecular structure,” said Haley, a professor in the Department of Chemistry and Biochemistry. “We have morphed our interest into the area known as spintronics.”

Initially, Dressler said, the team saw evidence of a persistent singlet diradical state in their new molecule but could not definitively show that the triplet state could be achieved.

“The nail in the coffin was when our collaborators in Spain were able to modify a spectrometer to detect the population of the triplet state at elevated temperatures,” Dressler said.

That temperature, at about 350 degrees Fahrenheit, is unprecedented for a diradical structure, Haley said, making such molecules more practical for use in electronic data-storage devices or molecular batteries, he said.

“While it was really cool to discover this kind of molecule, it was not the groundbreaking result,” Dressler said. “The implications are what is important. We might be able to tune this energy characteristic in a way never done before and make it applicable to a real-world setting.”

Two years ago, in the same journal, researchers in Haley’s lab reported the synthesis of a stable carbon-based molecule that changed its bonding patterns to a magnetic diradical state slightly above room temperature and then reverted to a nonmagnetic state below room temperature without decomposition. That accomplishment was seen as potentially useful in solar cells and some electronic devices that don’t require a lot of heat to change states.

The lab, Haley said, is closing in on newer structures of organic molecules whose temperature-flipping ranges are falling in line for potential application in more diverse electronics.

Organic molecules are widely used in some products already, including big-screen televisions and smartphones in which electrons are simply transferred from one molecule to another. They are believed to have potential for use in more complicated devices for use in medicine, environmental health and safety, and national security.

“These could be really cool for data storage,” Dressler said. “That’s way down the road. This research is helping to lay the groundwork.”

The National Science Foundation supported the work in Haley’s lab. Additional funding to the co-authors came from Mineco, an international group based in Europe that is focused on the natural resources sector, the Spanish government, Generalist Valenciana and the Japan Society for the Promotion of Science.

—By Jim Barlow, University Communications