Professor Su Shijian research group of South China University of Technology: application of thermal activation delay fluorescent materials based on adamantane modified acridine donor unit in organic light-emitting diodes

OLED technology has attracted the attention of academia and industry all over the world due to its outstanding advantages in large area, high quality display and lighting, ultra-high resolution, ultra fast response speed and flexible electronic applications Compared with the phosphorescent materials containing precious metals currently used in commercial OLED panels, pure organic luminescent materials with thermal activation delayed fluorescence (TADF) characteristics are potential materials that can achieve both 100% exciton utilization and low cost advantages Because TADF material has a very small single three line splitting energy (Δ EST), its singlet exciton (T1) can cross from RISC to S1 under the heat energy drive, and then produce the fluorescence radiation process, achieving 100% exciton utilization At present, tadf-oled has been able to achieve the same electroluminescence performance as OLED based on phosphorescent materials, and has become a hot candidate for the application of low-cost and high-efficiency OLED technology Recently, in view of the low luminous efficiency of some TADF molecules with double conformation, Professor Su Shijian, State Key Laboratory of light-emitting materials and devices, South China University of technology, designed a fluorescent guest molecule a-dmac-trz with adamantane modified acridine as electron donor and triphenyltriazine as electron acceptor (Figure 1A ）Although the molecule has double conformation, its external quantum efficiency (EQE) is still as high as 28.9% Relevant articles were published on angelw Chem Int ed (DOI: 10.1002 / anie 201811703) Figure 1 A) molecular structure of a-dmac-trz, b) quasi axial configuration, c) quasi equatorial configuration (source: angelw Chem Int ed.) Prof Su Shijian, male, 3, 1971 Yuesheng, doctor of engineering, Professor of School of materials science and engineering, South China University of technology, doctoral supervisor, fixed researcher of State Key Laboratory of light-emitting materials and devices He graduated from Xi'an Jiaotong University in 1993 and 1996 with bachelor's degree and master's degree respectively He studied abroad in 1998 and graduated from Yamagata University in Japan in March 2002 with a doctor's degree in engineering In April of the same year, he was supported by the research award fee of Japan Association for academic revitalization, and engaged in two-year postdoctoral research in the research room of world-famous OLED scientist Professor Chuner Cheng Since April 2004, he has been a researcher of Japan light industry technology revitalization Association, and then successively served as an assistant researcher of Yamagata University and an assistant professor of Yamagata University in Japan In September 2009, he returned to China for his current post The main research direction is organic electroluminescent materials and devices, which are selected into the "New Century Excellent Talents" support program of the Ministry of education, the winner of the national fund for Distinguished Young Scholars, and the chief scientist of the national key research and development program "new generation organic electroluminescent materials and devices" Frontier research achievements: the application of thermal activation delay fluorescent materials based on adamantane modified acridine donor unit in organic light-emitting diodes A-dmac-trz molecules exhibit very special double blue light emission in solution, with emission peaks at 419 nm and 479 nm, respectively By DFT calculation, we find that there are two local minimum configurations on the ground state potential energy surface, namely quasi axial configuration and quasi equatorial configuration (Fig 1b and 1c) The ratio distribution of these two configurations can be calculated quantitatively by scanning the flexible potential energy surface Through the low temperature phosphorescence spectrum, we can get the energy level difference of the singlet excited state and the triplet excited state Through the analysis of transient fluorescence spectrum at room temperature, the author found that the quasi axial configuration of a-dmac-trz molecule has the characteristics of traditional fluorescence, while the quasi equatorial configuration has the characteristics of delayed fluorescence (Figure 2) Figure 2 Room temperature transient fluorescence spectrum (source: angelw Chem Int ed.) based on a-dmac-trz Molecular Electroluminescent device, at a doping concentration of 20 wt%, the maximum external quantum efficiency of 28.9% (Figure 3) is obtained, which is far higher than the efficiency of the electroluminescent device based on the double conformational light-emitting molecule reported in the previous literature Fig 3 A) electroluminescence spectrum of a-dmac-trz based electroluminescence device, b) current efficiency and external quantum efficiency (source: angelw Chem Int ed.) the author further studies the reason why a-dmac-trz based electroluminescence device can achieve such high efficiency The local triplet (3lea) energy level of the quasi axial configuration of a-dmac-trz molecule is slightly higher than that of the charge transfer triplet (3cte) energy level of the quasi equatorial configuration At a higher doping concentration, a new Dexter energy transfer channel is obtained This new energy transfer channel greatly improves the exciton utilization rate and the external quantum efficiency of electroluminescence (Figure 4) Figure 4 Schematic diagram of energy transfer between quasi axial configuration and quasi equatorial configuration of a-dmac-trz molecule (source: angel Chem Int ed.) Relevant research results are published in angel Chem Int.ed (DOI: 10.1002/anie.201811703) Dr Li Wei and Dr Cai Xinyi are the co first authors of this paper The related work was supported by the Ministry of science and technology of the people's Republic of China, the National Natural Science Foundation of the people's Republic of China, the Department of science and technology of Guangdong Province and the foundation for doctors Nowadays, people and scientific research have been paid more and more attention in the economic life China has ushered in the "node of science and technology explosion" Behind the progress of science and technology is the work of countless scientists In the field of chemistry, in the context of the pursuit of innovation driven, international cooperation has been strengthened, the influence of Returned Scholars in the field of R & D has become increasingly prominent, and many excellent research groups have emerged in China For this reason, CBG information adopts the 1 + X reporting mechanism CBG information, chembeangoapp, chembeango official microblog, CBG wechat subscription number and other platforms jointly launch the column of "people and scientific research", approach the domestic representative research group, pay attention to their research, listen to their stories, record their demeanor, and explore their scientific research spirit.