|One of the assembled organic LEDs based on push-pull systems. |
Photo credit: Ruslan Gadirov / TSU
Scientists at the Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences, and Ural Federal University have developed, synthesized, and studied a series of new fluorophores - push-pull systems (compounds with pronounced electron-donor and electron-acceptor parts) based on cyanopyrazine. Ural chemists in cooperation with colleagues from Tomsk State University showed that the presence of a cyano group in the substance significantly increases the efficiency of organic light emitting diodes (OLEDs) based on it. This opens the prospect of creating new materials to enhance the brightness of displays of smartphones, computers and televisions. An article describing the research and its results was published in the journal Dyes and Pigments.
In previous research work, chemists demonstrated that one of the most promising compounds as an acceptor (attracting electrons) part in push-pull systems is the pyrazine ring (another name is 1,4-diazine), a compound of nitrogen, hydrogen and carbon that has a significant electron-accepting effect.
A study of the properties of a wide range of 1,4-diazine-based push-pull systems revealed that the addition of a benzene ring to the pyrazine cycle (quinoxaline derivatives) can improve the efficiency and brightness of the OLEDs produced. At the same time, some of the OLEDs tend to exhibit thermally activated delayed fluorescence (TADF). This is evidenced by the increase in fluorescence lifetime.
According to Egor Verbitsky, the head of the research team, Director of the Institute of Organic Synthesis, Ural Branch of RAS, Researcher of the Laboratory of Medical Chemistry and Advanced Organic Materials of Ural Federal University, it is well known that the introduction of additional electron acceptor - cyano group - in the light-emitting compounds (fluorophores) leads to improved TADF properties and increased overall OLED efficiency.
"Therefore, we modified the pyrazine-based push-pull system with cyano group and studied how this affected the photophysical properties of the fluorophores and the performance of OLEDs based on it. The TADF phenomenon, due to the peculiarities of the structure of the starting substance, did not occur (although there are prerequisites for it). However, it turned out that the introduction of a cyano group intensifies intermolecular interactions, as a result, not individual molecules but complexes of molecules begin to fluoresce. As a consequence, the luminescence intensity increased from 2.4 to 20 times, and the brightness of the emitted light increased up to 75 times. Several prototype devices made by our colleagues and co-authors from Tomsk State University showed such results. It is also important that we use inexpensive and accessible compounds in our research," reports Egor Verbitsky.
The research was supported by the Ministry of Science and Higher Education of the Russian Federation as part of the State Assignment (Project No. AAAA-A19-1190117900132-7).
Source/Credit: Ural Federal University