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Chemistry: A sophisticated process stacks dye molecules in such a way that their luminosity increases significantly as their size grows – a significant step forward for the electronics of tomorrow.
In nature, a certain size is often a prerequisite for biomolecules to perform their specific functions. For example, for proteins or DNA to fulfil their vital tasks, they must be folded in a precise manner – and this requires a certain minimum length.
Chemists in the laboratory have long been able to achieve the step-by-step construction of proteins and nucleic acids with defined lengths and compositions using solid-phase synthesis.
Now, for the first time, German and Korean researchers have presented a comparable synthesis method for organic dye molecules. Up to 14 perylene bisimide units can be specifically stacked on top of one another using this method. These dyes were chosen because they are of interest for future generations of organic semiconductors and nano-lasers. They begin to glow when excited by light pulses.
The discovery: luminosity increases dramatically
“With our new synthesis method, we can ensure that the dye molecules are not stacked irregularly, but are precisely folded into so-called ‘foldamers’ – in a defined sequence and spatial arrangement,” says Professor Frank Würthner, Head of the Center for Nanosystems Chemistry and Chair of Organic Chemistry II at the University of Würzburg.
But that is not all. As the scientists gradually stacked the dye molecules on top of one another, they discovered a crucial effect: by extending the stacks to a height of four to six units, their luminescence increases significantly.
Why is this the case? “In the range of four to six stacked molecules, the structure stabilises to such an extent that a multiexciton state dominates at the centre, leading to a significantly increased fluorescence quantum yield,” explains PhD student Leander Ernst, the study’s lead author. The increasing structural rigidity at the centre of the stack shields the excited state from external influences and optimises light emission.
The researchers’ data impressively demonstrate this effect: whilst a stack of two units exhibits a luminous efficiency of 47 %, this figure climbs to as much as 75 % for a chain of 14 units.
For future applications in technology, this means that components with stacked dyes could consume less electricity or shine significantly brighter for the same energy input.
What the study means for science
In the development of organic semiconductor materials, scientists have so far mostly used ‘dimer models’ to predict the coupling of molecules in solid-state materials, as found in materials science applications. It should now be clear that this model is insufficient – it is like trying to understand the structural stability of a house by examining two bricks placed on top of one another.
A key problem in the use of dye-based materials in lighting applications has hitherto been so-called quenching: normally, dyes lose their luminosity when packed closely together – they ‘extinguish’ one another. The researchers from Würzburg and Seoul have now overcome this limitation for the described perylene bisimide foldamers.
Nevertheless, the transfer from basic research to real-world everyday devices remains a challenge. A Würzburg research consortium combining chemistry and physics, led by Professors Tobias Brixner (Chemistry) and Bert Hecht (Physics), intends to address this issue at JMU.
The results were produced in collaboration between Professor Frank Würthner’s team and the group led by Professor Dongho Kim at Yonsei University in Seoul (Korea). They have been published in the journal Nature Chemistry.
Prof. Dr. Frank Würthner, frank.wuerthner@uni-wuerzburg.de
Generating extended foldamer dye stacks and unravelling their evolving exciton dynamics. Leander Ernst, Yongseok Hong, Hongwei Song, Wei Zhang, Elisabeth Lass, Dongho Kim & Frank Würthner. Nature Chemistry, 23. März 2026, DOI: 10.1038/s41557-026-02082-0
On the left, the step-by-step synthesis of structurally well-defined dye stacks. On the right, the o ...
Source: Leander Ernst
Copyright: University of Würzburg
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