Trifluoromethyl Radicals Tune Up Organic Electronics

Organic-based materials are increasingly being used to replace silicon- and metal-based components in optoelectronic devices—the organic materials are typically lighter weight, more flexible, and lower in cost. Scientists have recognized that strong electron-withdrawing groups such as trifluoromethyl enhance the electronic properties and improve the stability of the organic materials, which include polycyclic aromatic hydrocarbons (PAHs). But so far, none of the synthetic routes to add CF₃ groups to PAHs is optimal. A team of Colorado State University and Pacific Northwest National Laboratory scientists led by Colorado State’s Olga V. Boltalina and Steven H. Strauss has now discovered an efficient way to attach CF₃ groups to anthracene, pyrene, and other PAHs without the need for solvents, catalysts, or promoter reagents (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201300085). The researchers used gaseous CF₃I at elevated temperature to generate CF₃ radicals, which add to several positions on the PAH core. The electron-acceptor properties of the modified PAHs show a linear, predictable increase with each added CF₃ group, Strauss notes, which will allow researchers to tune PAH properties for specific applications. The new PAHs will figure prominently in ongoing studies of organic photovoltaics, he adds, and the researchers are discussing scaling up the syntheses with specialty chemical companies.