Chain length that determines the color of the molecule

These polymers, found here under UV light, are composed of exactly the same ingredients. The only difference is the length of the chain. Credits: Suiying Ye / ETH Zurich

Currently, a huge amount of research and development work is being carried out around the world on carbon-containing molecules or organic molecules that emit colored light after proper excitation. This field of study is driven by the display industry and the development of biomedical imaging technology. Accurate color adjustment of organic fluorescent dyes has traditionally been achieved by mixing different molecules, but ETH researchers have taken an approach that allows intramolecular chemical adjustment to produce a wide palette of colors. Developed.

Professor Jean-Christophe Leroux’s group leader, Yinyin Bao, and his team of scientists turned to fluorescent organic polymers for this study. It is best to think of these polymers as moving chains of varying lengths. “The chain has a symmetrical structure, two of which contribute to fluorescence,” explains Bao. “One component, called the fluorophore, is located in the center of the chain, and the other component is at each of the two ends of the chain.” In the center of the chain, the fluorochrome molecule and each end of the chain. Combining is a link of numbers and structures that scientists can adjust. When the polymer chain is bent so that one of its ends is close to the fluorophore and at the same time the chain is exposed to UV light, it fluoresces.

Distance affects interaction

Scientists have now been able to show that the fluorescence color depends not only on the structure of the chain links and ends, but also on the number of chain links. “The fluorescence of these polymers is due to the interaction of the ends of the chains with the fluorochrome molecules,” says Bao.

Researchers can control the number of chained links using a method called living polymerization. First, the chain grows slowly through a slow process that binds the components to the fluorophore. Once the required length is reached, scientists can terminate the process and at the same time generate the terminal molecule of the chain. This is how researchers have produced polymers of different colors. With less than 18 components, the molecule fluoresces yellow. 25 Green with chain link. And blue if there are more than 44 links. “What’s special about this is that these different luminescent polymers are all made up of exactly the same ingredients. The only difference is the length of the chain,” says Bao.

Wide color gamut OLED

A research team, including Professor Chih-Jen Shih’s group and scientists from the Royal Melbourne Institute of Technology in Australia, published their findings in a journal. Science AdvancesCurrently, researchers can produce fluorescent polymers of yellow, green, and blue, but are working on extending the principle to include other colors, including red.

These new fluorescent polymers are not high enough in electrical conductivity and cannot be used directly as display OLEDs (organic LEDs). However, it should be possible to combine polymers with semiconductor molecules in order to produce OLEDs with a wide color range in a simple way. When used in solar thermal power plants, it can also collect sunlight more efficiently, increasing the efficiency of the power plant. Bao considers key application areas for laboratory diagnostic procedures using fluorescence (such as PCR) and microscopic and image processing procedures in cell biology and medicine. Another potential use is as a security feature for banknotes, certificates, or passports.

See: “Continuous Color Tuning of Single Fluorophore Emissions by Spatial Charge Transfer Through Polymerization”, Suiying Ye, Tian Tian, ​​Andrew J. Christofferson, Sofia Erikson, Jakub Jagielski, Zhi Luo, Sudhir Kumar, Chih-Jen Shih, Jean-Christophe Leroux and Yinyin Bao, April 7, 2021 Science Advances..
DOI: 10.1126 / sciadv.abd1794 Chain length that determines the color of the molecule

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