My watch list


Making monitors brighter

A way to control the colour of OLEDs

Dominic Raithel

On the left, a polymer with an elongated backbone (red-yellow). The long side chains (grey) of the molecular building blocks form a scaffold that stabilizes the elongation. On the right, a polymer with a bent backbone.

27-Mar-2018: Organic light-emitting diodes (OLEDs) are used in smartphones and televisions to facilitate the high-contrast display of colours. Conjugated polymers are also often employed as organic semiconductors in such diodes. Researchers at the University of Bayreuth have found out how the spatial structure of these polymers can be used to control the colours of the OLEDs and help to increase the brightness of monitors.

Polymers with a backbone: spatial structures determine the colour of light

Polymers that are well-suited for use in organic light-emitting diodes play a central role in the new research findings. Thanks to the chain formed by connecting molecular building blocks, they possess a backbone. If the polymers are then exposed to a laser beam, they absorb the light and store it as excitation energy. This energy spreads along the backbone. Shortly after that, it is released by emission of light.

Up to now it had been assumed that the colour of the emitted light depends on how far the excitation energy spreads along the polymers: supposedly, the more bent the polymers were, the smaller the distance over which the energy spread. However, the scientists in Bayreuth have now refuted this assumption. The polymers they studied have backbones that are chemically identical and bent to different degrees, but the excitation energy always spreads over the same distance. Bent polymers emit green or blue light, while elongated polymers radiate yellow or red light. “When these polymers come to be used in organic light-emitting diodes, their various spatial structures can be utilized to precisely control the colour of the light emit from the OLEDs,” explained physicist Dominic Raithel (M.Sc.).

The researchers in Bayreuth also found out that the elongated polymers possess a scaffold formed by its side chains, which stabilizes the elongated structure. “This results in a special advantage for light-emitting diodes: when elongated polymers are layered on top of one another, the scaffolds provide stability. Optical emission is not thereby weakened“, said Raithel, who recently completed his dissertation in the University of Bayreuth’s DFG-funded research training group “Photophysics of Synthetic and Biological Multichromophoric Systems”. In this context, natural and synthetic organic materials are studied in close interdisciplinary cooperation. For example, experimental physicists Prof. Dr. Anna Köhler and Prof. Dr. Jürgen Köhler along with Prof. Dr. Mukundan Thelakkat, expert in functional polymers, were involved in the new experiments.

A transatlantic interplay of theory and experiment

The comparative experimental investigations of polymers made use of different types of spectroscopy methods. “A decisive factor was single-molecule spectroscopy at very low temperatures, for which Bayreuth provided us with its high-performance infrastructure. Using this method, we were able to determine the colour of the emitted light and finally the extension of excitation energy over the chain-like polymers,” explained Dr. Richard Hildner, who coordinated the research at the University of Bayreuth.  

The scientists in Bayreuth worked together closely with a research group at Rice University in Houston, Texas. Dr. Lena Simine and Prof. Dr. Peter J. Rossky carried out extensive calculations on the impact of polymer structures on the colour of the emitted light. Linking experimental and theoretical methods led to insights into the spatial structures of individual polymer chains which would have been impossible using traditional imaging techniques.

Original publication:
Dominic Raithel, Lena Simine, Sebastian Pickel, Konstantin Schötz, Fabian Panzer, Sebastian Baderschneider, Daniel Schiefer, Ruth Lohwasser, Jürgen Köhler, Mukundan Thelakkat, Michael Sommer, Anna Köhler, Peter J. Rossky and Richard Hildner; "Direct observation of backbone planarization via side-chain alignment in single bulky-substituted polythiophenes"; PNAS; 2018

Facts, background information, dossiers

  • smartphones
  • OLED materials
  • organic light-emitt…
  • light emitting diodes
  • polymers
  • functional polymers
  • Polythiophene polymers
  • polythiophenes

More about Uni Bayreuth

  • News

    Biologists develop new method of cloning

    DNA, which contains the genetic information of an organism, consists of long “chains” of nucleotides. In order to study the functions based on the sequence of these building blocks, DNA molecules must be inserted in carrier molecules (plasmid-vectors) to be multiplied. For this cloning proc ... more

    Chaos that will keep you warm: Researchers improve heat insulation using deliberate chaos

    Powder is extremely well-suited for thermal insulation when there is a jumble of different sized nanoparticles in it. This was discovered by a research group at the University of Bayreuth led by Prof. Dr. Markus Retsch. The scientists were able to determine how the thermal conductivity of p ... more

    New insights about our Earth’s lower mantle

    Using DESY's bright X-ray light source PETRA III, a team of scientists has discovered unexpected facts about the most abundant mineral on Earth. The mineral bridgmanite makes up roughly one third of Earth’s entire volume and is the major component of Earth’s lower mantle. Thus, its physical ... more

  • q&more articles

    Authentic food

    Authentic food is growing in popularity with consumers. In a heavily industrialized market, a regional, single-source and/or specially manufactured product is increasingly becoming a guarantor of greater value. In the premium segment in particular, economically motivated “food fraud” can re ... more

    More than honey?

    For thousands of years, the word “honey” has been synonymous with an all-natural, healthy food. Unsurprisingly, honey has also enjoyed unwavering popularity with consumers – and especially in times when organic food and a healthy lifestyle are more in vogue than ever before. more

    What Are We Eating?

    What ends up on our plates? We used to think we knew – until we were disabused of this notion in early 2013. Instead of beef, there had been large-scale use of processed horsemeat, especially in frozen products and mincemeat. Although this posed no hazard to health, the damage was enormous, ... more

  • Authors

    Dr. Christopher Igel

    completed his undergraduate studies in biochemistry at the University of Bayreuth from 2009 to 2013. He completed his bachelor’s dissertation entitled “Honey Analysis Using NMR” at the BIOmac research centre under the tutelage of Prof. Dr. Schwarzinger. more

    Wolfrat Bachert

    commenced his undergraduate studies in mechanical engineering at TU Dresden before moving to the University of Bayreuth in 2009 to study biology. In 2013, he completed his bachelor dissertation in the Dept. of Biochemistry under the tutelage of Prof. Dr. Wulf Blankenfeldt on the subject of ... more

    Prof. Dr. Stephan Clemens

    Stephan Clemens, Jg. 1963, studied biology in Münster and Brighton, then acquired his doctorate in Münster. Since his postdoc-stay at the University of California San Diego, his scientific interest has been mainly targeted at metal homoeostasis in plants. He uses the models Arabidopsis thal ... more

q&more – the networking platform for quality excellence in lab and process

The q&more concept is to increase the visibility of recent research and innovative solutions, and support the exchange of knowledge. In the broad spectrum of subjects covered, the focus is on achieving maximum quality in highly innovative sectors. As a modern knowledge platform, q&more offers market participants one-of-a-kind networking opportunities. Cutting-edge research is presented by authors of international repute. Attractively presented in a high-quality context, and published in German and English, the original articles introduce new concepts and highlight unconventional solution strategies.

> more about q&more

q&more is supported by:


Your browser is not current. Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE