Synthesis And Characterization Of Solution Processed Hyper-structured Thermally Activated Delayed Fluorescence Materials-Based On Triazine Derivatives

Thermally activated delayed fluorescence（TADF）materials are known as the third generation of organic light-emitting materials,which are capable of efficient reverse intersystem crossing（RISC）from the triplet excited state（T₁）to the singlet excited state（S₁）to use triplet excitons for photoluminescence with theoretically100%exciton harvesting in emission,have been widely used in the field of organic light emitting diodes（OLEDs）.Compared with the vacuum evaporation devices,solution-processed TADF device has the advantages of low cost and large-area production,which has attracted widespread attention.In this paper,a hyper-structured hole transport material CRA-mCP,two kinds of triazine-based hyper-structured TADF emitters CRA-PXZ-Trz and CRA-Cz-Trz,and two kinds of model compounds RES-mCP and RES-PXZ-Trz were designed and synthesized for solution-processes.The chemical structures and properties of objective coumpounds and intermediates were characterized by proton nuclear magnetic resonance（¹H NMR）,fourier transform infrared spectra（FT-IR）,elemental analyzers（EA）,high-resolution mass spectra（HR MS）,matrix-assisted laser desorption ionization time-of-fight mass spectra（MALDI-TOF MS）,X-ray diffractionanalysis（XRD）,thermogravimetric analysis（TGA）,differential scanning calorimeter（DSC）,UV-Visibleabsorption spectra（UV-Vis）,photoluminescence spectra（PL）,cyclic voltammetry,etc.Spin-coating as-parepared materials as emitters or hole-transporting material,OLED were fabricated and measured.In Part 1,hyper-structured host material CRA-mCP and model compound RES-mCP were synthesized and characterized.Firstly,a small molecule mCP-N₃ with the azide end group,a calix-4-resorcinarene derivative（CRA-Alkyne）with eight alkynyl end groups,and a resorcinol derivative（RES-Alkyne）were synthesized.CRA-mCP,the target hyper-structured material was synthesized via“click chemistry”reaction between the azide group of mCP-N₃ and the alkyne group of CRA-Alkyne（or RES-Alkyne）.MALDI-TOF-MS and EA test results showed that CRA-mCP and RES-mCP molecules were successfully synthesized,and the introducted rate of functional molecules was nearly 100%.The temperature of glass transition（T_g）of CRA-mCP is 148°C determined by DSC.The solution precessed device with the CRA-mCP as hole transport layer showed a maximum current density of 14.0mA/cm² and maximum brightness of 3954 cd/m².In part 2,triazinyl-based hyper-structured green TADF material CRA-PXZ-Trz and model compound RES-PXZ-Trz were synthesized and characterized.Firstly,the TADF functional group PXZ-Trz-N₃ was synthesized by Suzuki and diazotization reactions.Then,the hype-rstructured TADF molecule CRA-PXZ-Trz and the model compound RES-PXZ-Trz were synthesized by azide-alkyne“click”reaction.The results of HR MS indicated that the functional group PXZ-Trz-N₃ was successfully synthesized.The¹H NMR,FT-IR,and EA test results indicated that the functional groups were successfully introduced to CRA core and the introduced rate was nearly100%.DSC result showed that the CRA-PXZ-Trz has no glass transition temperature,indicating that the molecule showed amorphous state.TGA results showed that CRA-PXZ-Trz has good thermal stability（T_d=294°C）Using CRA-PXZ-Trz droped with mCP as light-emitting layer,the device gave an green emission with a maximum current efficiency of 26.9 cd/A and maximum brightness of 2424 cd/m².In part 3,a blue TADF molecule Cz-Trz and hyper-structured TADF CRA-Cz-Trz were synthesized and characterized.Firstly,a blue emitter Cz-Trz(λ_PL=430 nm)and a functional compound Cz-Trz-N₃ with an azide end group were synthesized.Then,the Cz-Trz-N₃ was bonded to the periphery of the CRA core through“click”reaction to synthesize blue hyper-structured TADF molecule CRA-Cz-Trz(λ_PL=425 nm).The ¹H NMR,FT-IR and EA test results indicated the introduction of functional components was nearly 100%.TGA results showed that CRA-Cz-Trz has good thermal stability（T_d=244°C）.And the CRA-Cz-Trz-based devices are still being tested.