Theoretical Study On The Performance Improvement And Intersystem Crossing Rates Of Two TADF Materials

Since Adachi et al.reported high performance of organic light-emitting diodes(OLED)devices based on thermally activated delayed fluorescence(TADF)materials in 2012,the design and synthesis of novel TADF materials with different molecular structures have attracted extensive attention.TADF materials,which are known as the most promising third-generation optoelectronic materials,have been able to capture triplet excitons through the reverse intersystem crossing(RISC)process to make the internal quantum efficiency(IQE)close to 100%.In our work,we performed the theoretical study on two new TADF emittors,9,10-bis(4-(9H-carbazol-9-yl)-2,6-dimethylph-enyl)-9,10-diboraanthracene(CzDBA)and 7-phenylquinolino[3,2,1-de]acridine-5,9-dione(7-PHQAD).We calculated the luminescent properties and intersystem crossing rates and explored the in-depth luminescent mechanism theoretically.This thesis is mainly divided into two parts.The first part includes two chapters which introduce the research background and theoretical methods.Starting from the introduction about the development process of organic photoelectric materials such as TADF materials,hot exciton materials and phosphorescent materials,we mainly summarized the recent progress and the design strategies of TADF materials and categorized commonly used donors/acceptors.The second chapter mainly introduces the theoretical methods for the electronic and geometric structure calculations and the spectral and ISC rate simulation of TADF emittors.The second part also includes two chapters which are focused on my works.The third chapter discusses how to improve the fluorescence performance of TADF molecule CzDBA through halogen substitution.We carried out halogen substitution on the acceptor of CzDBA and obtained a series of novel TADF molecules with high performance.The fourth chapter presents the qualitative description of intersystem crossing rate of TADF molecule 7-PHQAD.By taking the Herzberg-Teller(HT)vibronic couplingand Duschinsky rotation effects into account,we produced the experimental results.Our calculation revealed the the HT vibronic coupling effect predominants the experimental reverse ISC rate.In summary,this paper gives an overview of the development of OLED materials and introduces the theoretical calculation methods for optoelectronic properties.Through our specific case studies,we have demonstrated the reliability of related methods in the description of OLED emittors.The research in this article has guiding significance for the control and quantitative prediction of OLED performance.