How luminous animals could change the structure of OLEDs
Page 2: Different colors despite the same structure
This energy difference also influences the color: if it is low, the molecule glows red, if it is high, the light turns blue. "We can also influence the color through chemical manipulation." This works, for example, by stabilizing or destabilizing certain groups, i.e. chemical components of the molecule. "The functional groups consist of atoms, which in turn influence the electronic structure of the molecule," explains Schramm.
(Image: Stefan Schramm / Dieter Weiß)
Apart from the applications, the chemist also wants to understand the mechanisms behind the different molecular structures of the animals. "Luminous crustaceans use an entirely different chemical structure than, for example, the firefly," says Schramm. "Crustaceans tend to glow blue, while fireflies tend to glow green." At the same time, there are insects that use the same structure but glow very differently.
A lot already known about fireflies
The fact that living creatures could produce light themselves dates back to around 2.5 billion years before the present day, explained Schramm. "When oxygen first formed in the Earth's atmosphere, it was a problem for the organisms of the time, because oxygen acted like a cytotoxin." Nature was therefore looking for a way to break down the oxygen. "It is assumed that light was more of a by-product of the detoxification of oxygen." Over time, as a result of co-evolution, light has fulfilled other functions, such as warding off enemies in the deep sea or attracting mating partners.
Schramm does not use animals. For the application-oriented part, he draws on the wealth of knowledge about glowworms. "We already know the chemistry of firefly bioluminescence very well and know how to produce the molecules fully synthetically."
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In addition, fireflies are the system that, according to previous findings, glows most efficiently. Schramm explains that the brightness of a molecule is expressed in what is known as the quantum yield. This describes the percentage of molecules in a bioluminescence reaction that ultimately glow. In fireflies, this is 42 percent. "This is roughly in the range that can also be achieved with modern inorganic LEDs," says the scientist. The electrically excited luminescence of OLEDs is ideally 10 to 30 percent. The fireflies are therefore already more efficient than OLEDs. "This is precisely what we are trying to transfer to build more efficient OLEDs in the future," emphasizes Schramm.
Molecules should be ready for use in around five years
However, it will be several years before such a system is finally used, as research into BiOLEMs is still in its infancy. "Before we can build an OLED with the molecules, we first have to tailor and produce the molecules," says Schramm. His team is currently looking for public funding. "Based on this, we will carry out a research project, at the end of which we will have suitable molecules with a horizon of around four to five years, which we can then also be used to build OLEDs."
Incidentally, a bioluminescent animal has also been named "Mollusk of the Year 2024": The land snail Phuphania crossei, which is native to Thailand, continuously emits a greenish light like a living glow stick. People can see the glow even in daylight. Special trick: the snail can partially switch off the glow.
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