Design, Synthesis And Properties Of Thermally Activated Delayed Fluorescent Materials Based On Phenanthrene And Phenanthroline Derivatives

Organic light-emitting diodes(OLED)have become very popular emerging display and lighting devices in recent years.because of its self-luminous,fast response speed(1 μs magnitude),low energy consumption and wide visual range(more than 170°),it also has the characteristics of flexible display,clear and bright,thin(less than 2 mm),low cost and simple manufacturing process.The luminescent layer in the OLED goes through the traditional fluorescent and phosphorescent materials and ushered in the third generation of thermally activated delayed fluorescent materials(TADF),which have the characteristics of phosphorescent materials.Above all,pure organic TADF materials are free of noble metal atoms and belong to environment-friendly materials.Usually when preparing the OLED,the material is used after doping as the guest material with the subject material.one aspect is to prevent the concentration of the guest material from being too high and to produce the aggregation fluorescence quenching(ACQ)effect;the other aspect is to transfer energy from the subject to the guest,to produce Forster energy transfer and to improve the efficiency of the device.hence,it is particularly important to develop TADF materials with new structures.The purpose of this paper is to study the application of phenanthrene and phenanthroline derivatives in TADF materials through simple molecular design and to develop three series of pure organic D-A-D TADF materials.the thermal properties,photophysical properties,electrochemical properties,fluorescence quantum efficiency and lifetime of these compounds were also tested and studied.At the microscopic level,the molecular energy levels were calculated using density functional theory(DFT).these materials were applied to the OLED and test their device properties.The first chapter is the introduction part,briefly introduces the development course of the OLED,the classification and luminescence principle of organic luminescent materials,and emphasizes the history,classification and luminescence principle of TADF materials.Finally,the main research direction and research content of this paper are expounded.Three novel TADF molecules with D-A-D structure were synthesized in second chapter.Three target molecules were prepared by Buchwald-Hartwig coupling reaction with 2,3-diyanopyrazine as Acceptor,3,6-di(carbazole)-carbazole,3,6-di(phenoxazine)carbazole and 3,6-di(phenothiazine)-carbazole as Donor,respectively.All three materials have good thermal stability and high decomposition temperature.the maximum absorption wavelength of the three compounds is about 300 nm,and the intramolecular conjugated groups undergo π→π*electron transitions with high absorption intensity.the maximum emission wavelength is 500～600 nm and has high fluorescence quantum efficiency.the three materials all have deeper HOMO and LUMO energy levels with smaller Eg values.Through the performance test of the fabricated devices,the brightening voltage is 3.2V,the maximum external quantum efficiency is up to 10%,and the maximum luminous brightness is 8056 cd/m2,28cd/m2,7674cd/m2,all of them is yellowgreen light emitter,respectively the performance of the device has lower bright voltage,higher brightness and higher EQE,all meet the expected goal.In third chapter,three new structural TADF materials were successfully developed by a strong base(NaH)induced coupling reaction by using dipyridyl and[3,2-a:2’,3’-c]phenazine as the donor;carbazole,3,6-di(tert-butyl)carbazole,3,6-diphenyl carbazole as the acceptor.the Td of all three compounds exceeded 400℃,indicating that all three substances had good thermal stability.the maximum absorption wavelength of the three compounds is around 290-300 nm,and the intramolecular conjugated groups undergoπ→π*electron transitions with high absorption intensity.all three materials have high fluorescence quantum yield,and the luminescence position is in the yellow-green light range.By cyclic voltammetry,the HOMO,LUMO energy level of the material was tested,which is prepared to realize energy level matching and improve device performance.the performance of the first two devices is general,the external quantum efficiency fails to achieve the ideal effect,and the latter device performs well.All three devices have lower bright voltage and higher brightness.It is necessary to further optimize the device preparation process to achieve excellent performance.The fourth chapter works,two target compounds were successfully prepared using diphenylbipyridine phenazine as Acceptor,carbazole,3,6-di(tert-butyl)carbazole as Donor,by the Buchwald-Hartwig coupling reaction.the Td of both compounds was more than 400℃,indicating that all three substances had good thermal stability.Both materials have a maximum emission wavelength of more than 600 nm,can achieve red emission,fluorescence quantum efficiency performance is general.the △EST of the two materials is between 0.18～0.22 eV,which satisfies the properties of the TADF materials,and both materials have fluorescence quantum efficiency greater than 25%and have nanosecond,microsecond lifetime,which belongs to the TADF materials.both materials have small Eg values.by evaluating the properties of both materials,both meet the goal at the beginning of the design.Chapter five summarizes the work of this paper and looks forward to the development of OLED.