Translation. Region: Russian Federal
Source: Novosibirsk State University – Novosibirsk State University –
An innovative approach to the accelerated creation of materials with thermally activated delayed fluorescence (TADF), which can lead to a significant improvement in the characteristics of next-generation organic light-emitting diodes (OLEDs), was developed by researchers at the Laboratory of Low Carbon Chemical Technologies Faculty of Natural Sciences, Novosibirsk State University. The researchers presented a new method for modeling the properties of so-called multiresonant TADF emitters, which are characterized by a narrow spectral band and high luminescence efficiency, in the article “Quantum-Chemical Simulation of Multiresonance Thermally Activated Delayed Fluorescence Materials Based on B,N-Heteroarenes Using Graph Neural Networks,” published in the international journalThe Journal of Physical Chemistry A“.
— Organic light-emitting diodes are a modern technology that each of us encounters on a daily basis. For example, even now, reading this text from a smartphone or computer screen. Each pixel of the display is a small “bulb” that glows when an electric current is applied to it. The materials for such miniature “bulbs” are completely organic emitter molecules consisting of carbon, hydrogen, nitrogen, oxygen and sometimes other chemical elements. Due to their organic nature, such materials make it possible to make very light, bright, contrasting and energy-efficient displays for smartphones, laptops, smart watches and many other devices. The world is actively searching for such new effective materials that can be used in OLED technology. Computer modeling allows us to predict many properties with fairly good accuracy and study the properties of molecules in silico before they are synthesized in a flask. Such studies are also conducted in our laboratory, — explained the head of the Laboratory of Low-Carbon Chemical Technologies of the NSU Natural Sciences (ORËL ResearchLab) Evgeny Mostovich.
The new study, conducted by junior research fellows of the laboratory Daria Tarakanovskaya and Evgeny Mostovich, focuses on the development of materials using advanced modeling methods with the use of graph neural networks. These networks allow for the efficient prediction of optoelectronic properties of molecules, which significantly accelerates the process of developing new molecules. The basis for the creation of new emitters were multiresonant molecules, which, due to the uniqueness of their structure, demonstrate improved fluorescence properties.
— Modern OLED emitters are a pair of electron donor and electron acceptor groups connected via a bridge. This union of donor and acceptor provides a minimal difference in energy between the two excited states of such a molecule — singlet and triplet — and allows transforming all “dark” (non-emitting) triplet states into singlet states capable of emitting light by TADF. However, such a design has a significant drawback, since the donor and acceptor parts are not rigidly connected to each other, and the geometries of the excited and non-excited states are very different, a lot of energy is spent on this change, leading to a broadening of the emission spectrum of the molecule. The width of the spectrum directly affects the color perception of the pixel, for example, it becomes not blue, but blue-green, — said Daria Tarakanovskaya.
In their research, the developers of the method used a new type of dyes – multiresonance. In them, the donor and acceptor are presented not as functional groups, but as atoms. For example, nitrogen and boron, linked in a certain way into one carbon skeleton. This creates a very rigid structure, and the alternation of boron and nitrogen atoms leads to the multiresonance effect and allows obtaining effective emitters with a narrow emission band. However, classical quantum-chemical modeling of such dyes requires very resource-intensive computational methods, so the scientists decided to use graph neural networks.
— We are striving to create materials that could significantly increase the efficiency of OLEDs by taking advantage of the multiresonance effect. The results of our study show that the use of graph neural networks can significantly speed up the design process of new multiresonance TADF emitters, which opens up new opportunities for creating more efficient and durable devices, — explained Evgeny Mostovich.
An important aspect of the study was the study of the influence of the structure of molecules (specify, molecules of what) on the nature of triplet and singlet states, as well as their energy, which is critical for increasing the speed of TADF. Scientists have found that adding oxygen and sulfur atoms to the structure of such molecules enhances this interaction, and this in turn leads to improved radiation characteristics and an increase in the quantum yield of photoluminescence. Thanks to the developed method, scientists have selected a number of the most promising molecules, and now synthetic chemists, who have already obtained the first result, will take up the matter. The molecule they synthesized has a bright green fluorescence with a very narrow emission band of only 25 nm. Now the goal is blue and red colors, which are so necessary for a full-color OLED display.
The work was carried out within the framework of a project supported by the Ministry of Science and Higher Education of the Russian Federation. It opens up new prospects in the field of developing organic light-emitting diodes with high color purity and efficiency. This project has the potential to significantly contribute to the development of lighting technology and electronics, offering more efficient solutions for future display and lighting technologies.
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