Molecule Could Advance Displays

The first stable derivative of nonacene has been synthesized, creating a compound that holds significant promise in the manufacture of flexible organic electronics such as large displays, solar cells and radio-frequency identification tags (RFIDs).

The University of New Hampshire team that performed the work was led by professor of organic chemistry and materials science Glen Miller and including two UNH undergraduates.

Nonacene, a compound with nine rings of benzene fused in a linear fashion, belongs to a class of organic semiconductors called acenes, widely recognized to be among the best in terms of electronic performance. Yet they are highly unstable — oxidizing rapidly.

"We have known that nonacene would have very desirable electronic properties, but it was just a tease, because you couldn't make it, you couldn't use it," said Miller, who has been working to prepare large acenes since 2007.

He and his team — research scientist Irvinder Kaur, postdoctoral fellow Mikael Jazdzyk, and UNH seniors Polina Prusevich and Nathan Stein — built the large nonacene derivative from smaller pieces, the way one might build a Lego structure. The key to the molecule’s stability is the addition of arylthio functional groups, stable collections of atoms that contain sulfur.

“The skeleton of the molecule is still there, but it's got additional functional groups attached to the skeleton," Miller said. This not only made the derivative stable, but also made it soluble, further enhancing its usefulness.

A significant technical barrier (i.e., facile oxidative degradation) that has prevented the preparation of large acenes has now been breached. Using a combination of experimentally and theoretically derived substituent effects, the design, synthesis, isolation, and characterization of the first persistent nonacene derivative is described. The molecular design strategy includes placement of arylthio (or alkylthio) substituents on the terminal rings of the nonacene skeleton, effectively converting an open-shell singlet diradical into a closed-shell system. These powerful substituent effects appear to be suitable for the synthesis of other persistent, soluble, large acene derivatives required for advanced thin-film organic semiconductor applications. (Image Copyright © 2010 American Chemical Society)

Nonacenes hold promise for further development of flexible organic electronic devices: computer displays so thin they could be rolled up or even worn. Miller noted that the military is interested in the technology that would allow for chameleonlike camouflage clothing that could change with the environment.

Organic solar cells are another potential application of nonacenes; such cells could cut the cost of solar power by making use of inexpensive organic molecules rather than the expensive crystalline silicon that is used in most solar cells. Although Miller noted that his team's work is but a first step toward creating stable nonacene devices, "these compounds push all of these technologies further."

"Before our work, the thought of preparing flexible organic electronic devices using nonacene or a nonacene derivative was just a dream," he said. "With this major step forward, we are much closer to realizing the dream."

Funding was provided by the National Science Foundation through the Nanoscale Science & Engineering Center for High-Rate Nanomanufacturing.

The findings were published in January in the Journal of the American Chemical Society.

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