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New boron compounds for organic light-emitting diodes

Luminescent blue boron-containing nanographenes are highly promising materials for portable electronic devices

5 Jun 2015 | Editor

Chemists at the Goethe University have now developed a new class of organic luminescent materials through the targeted introduction of boron atoms into the molecular structures. The compounds described in the professional journal Angewandte Chemie (Applied Chemistry) feature an intensive blue fluorescence and are therefore of interest for use in OLED displays.

Carbon in the form of graphite conducts the electrical current in a similar way to a metal. In addition, its two-dimensional shape, the graphene layer, has extremely attractive optical and electronic properties. In graphene, the discoverers of which were awarded the Nobel Prize for Physics in 2010, countless benzene rings are fused to form a honeycomb structure. Sections of this structure, so-called nanographenes or Polycyclic Aromatic Hydrocarbons (PAHs), constitute an important basis of organic electronics.

Goethe University - Luminescent blue boron-containing nanographenes

Figure: Goethe University - Luminescent blue boron-containing nanographenes

A comparison of the new boron-containing nanographenes with the analogous boron-free hydrocarbons verifies the fact that the boron atoms have a decisive impact on two key properties of an OLED luminophore:

  • the fluorescence colour shifts into the highly desirable blue spectral range
  • the capacity to transport electrons is substantially improved

To date, only limited use could be made of the full potential of boron-containing PAHs, since most of the exponents are sensitive to air and moisture.

Valentin Hertz, who synthesised the compounds within the scope of his doctoral dissertation, said, "This problem does not occur with our materials, which is important with regard to practical applications."

Hertz and Wagner anticipate that materials such as the graphene flakes they have developed will be particularly suitable for use in portable electronic devices. As film displays for future generations of smartphones and tablets, even large-scale screens could be rolled up or folded to save space when the devices are not in use.

Prof. Matthias Wagner of the Institute for Inorganic and Analytical Chemistry at the Goethe University, said, "For a long time, efforts were largely focused on affecting the properties of nanographenes by chemically manipulating their edges." Prof. Matthias added, "However, in recent years, researchers have been increasingly capable of also modifying the inner structure by embedding foreign atoms in the carbon network. This is where boron assumes crucial significance."

Boron-Containing Polycyclic Aromatic Hydrocarbons: Facile Synthesis of Stable, Redox-Active Luminophores

M. Sc. Valentin M. Hertz | Dr. Michael Bolte | Dr. Hans-Wolfram Lerner | Prof. Dr. Matthias Wagner

Article first published online: 8 JUN 2015 | DOI: 10.1002/anie.201502977

Abstract

Herein we show that replacing the two meso carbon atoms of the polycyclic aromatic hydrocarbon (PAH) bisanthene by boron atoms transforms a near-infrared dye into an efficient blue luminophore. This observation impressively illustrates the impact of boron doping on the frontier orbitals of PAHs. To take full advantage of this tool for the targeted design of organic electronic materials, the underlying structure–property relationships need to be further elucidated. We therefore developed a modular synthesis sequence based on a Peterson olefination, a stilbene-type photocyclization, and an Si–B exchange reaction to substantially broaden the palette of accessible polycyclic aromatic organoboranes and to permit a direct comparison with their PAH congeners.

www.uni-frankfurt.de   


About Goethe University Frankfurt

Goethe University has a strong background in research and is based in the European financial center of Frankfurt. Founded in 1914 with purely private funds by liberally-oriented Frankfurt citizens, it is dedicated to research and education under the motto "Science for Society" and to this day continues to function as a "citizens' university". Many of the early benefactors were Jewish.

Over the past 100 years, Goethe University has done pioneering work in the social and sociological sciences, chemistry, quantum physics, brain research and labour law. It gained a unique level of autonomy on 1 January 2008 by returning to its historic roots as a "foundation university". Today, it is among the top ten in external funding and among the top three largest universities in Germany, with three clusters of excellence in medicine, life sciences and the humanities.

Source: Goethe University Frankfurt


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