A Nonacene With Staying Power

The first persistent derivative of nonacene—a compound with nine aromatic rings fused in a linear fashion—has been prepared by chemists at the University of New Hampshire (J. Am. Chem. Soc., DOI: 10.1021/ja9095472). With high-charge-carrier mobilities, acenes are promising organic semiconductors for thin-film transistors, displays, and photovoltaics. Smaller acenes, such as pentacene, have already found use in organic light-emitting-diode displays, for example. Larger acenes potentially have even higher mobilities, but the compounds oxidize rapidly. Glen P. Miller, Irvinder Kaur, and coworkers found that they could impede this degradation by adding arylthio groups to nonacene. Density functional theory calculations predict that these substituents alter nonacene’s electronics, Miller says, “effectively converting a ground-state singlet diradical into a closed-shell species while simultaneously reducing the HOMO-LUMO gap to about 1 eV.” Miller hopes to perform a detailed computational study of how substituents affect the total spin and molecular orbital energy gaps in larger acenes. Preparing very large, persistent acenes “is an intellectually tantalizing and increasingly realistic goal,” he says.