Boron Turns Graphene into Blue Light Emitter

Chemists at Goethe University Frankfurt have developed a new class of organic luminescent materials through the targeted introduction of boron atoms into graphene. The compounds exhibit an intense blue fluorescence and, consequently, are of interest for use as organic LEDs (OLEDs).

Within graphene, benzene rings are fused to form a honeycomb structure. Sections of this structure, referred to as nanographenes or polycyclic aromatic hydrocarbons (PAHs), play an integral role in organic electronics. Within the study, boron atoms specifically replaced the two meso carbon atoms within the PAH, which resulted in its ability to transform a near-infrared dye into a blue luminophore.

Customized organic molecules enable the production of lightweight, mechanically flexible electronic components adapted to individual applications, such as LEDs. Courtesy of Goethe University Frankfurt.

The boron-containing nanographenes have an impact on two key properties of an OLED luminophore, the researchers said: the color of fluorescence shifts into the highly desirable, blue spectral range and the capacity to transport electrons is substantially improved. To date, only limited use could be made of boron-containing PAHs, as most of the exponents are sensitive to air and moisture.

"This problem does not occur with our materials, which is important with regard to practical applications," said Valentin Hertz, who synthesized the compounds while writing his doctoral dissertation.

"For a long time, efforts were largely focused on affecting the properties of nanographenes by chemically manipulating their edges," said professor Matthias Wagner. In recent years, he said, researchers have become much more capable in their abilities to modify the inner structures by embedding foreign atoms within the carbon network. "This is where boron assumes crucial significance," he said.

Hertz and Wagner anticipate that such materials like the graphene flakes they developed will be particularly suitable for use in portable electronic devices, including future generations of film displays for smartphones and tablets.

The research was published in Angewandte Chemie (doi: 10.1002/anie.201502977).

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