Synthesis And Properties Of Thermally Activated Delayed Fluorescence Materials Based On Quinoxaline Derivatives

In recent years,thermally activated delayed fluorescence?TADF?materials have attracted much attentions of researchers in the field of organic electroluminescence,which is due to this type of material has a small singlet-triplet energy level difference(?E_ST),the triplet?T₁?excitons generated by electrical excitation can reach the singlet state?S₁?through reverse gap crossing?RISC?,through radiation,and then The transition mode returns to the ground state and emits delayed fluorescence,thus achieving a theoretical 100%exciton utilization rate.Therefore,TADF is considered to be the third generation of electroluminescent materials after phosphorescent materials,and has broad application prospects in the field of organic electroluminescent diodes in the future.A systematic review of TADF materials researches in this paper.For aiming at the key scientific issues of TADF few kind materials,low luminous efficiency,serious roll-off at high current density and unclear structure-properties relationship,etc.Herein,we designed and synthesized three novel series including eight TADF light-emitting materials.Their chemical structures of these TADF materials were well confirmed via ¹HNMR and ¹³C NMR spectroscopy,MALDI-TOF mass spectrometry.Meanwhile,their thermal properties,photophysical and electrochemical properties are investigated by thermogravimetric analysis?TGA?,steady and transient photoluminescent spectrometry,and cyclic voltammetry?CV?.The relationship between the molecular sturctures and properties will be revealed.Finally,OLEDs are fabricated through solution-process employing these TADF materials as guests.The main research contents and achievements of this dissertation are as follows:?1?.Two novel TADF materials,t Bu Cz Q and PTZQ,based on indole[2,3-b]quinoxaline as electron acceptor unit,phenothiazine and 3,6-bis?tert-butyl?carbazole as electron donor unit,are designed and synthesized to investigate the influence of different donor units on their photophysical and electrochemical properties and electroluminescent performance.The results indicate that both materials show blue-green emission in solution and solid film.In oxygen-free toluene solution,the delayed fluorescence lifetimes of t Bu Cz Q and PTZQ are 1.4?s and 1.1?s,respectively Based on PVK:OXD-7 as co-host materials and obtained materials as guest were fabricated with different dopant concentration,the t Bu Cz Q-and PTZQ-based devices showed a maximum external quantum efficiency(EQE_max)of1.06%with a peak at 485 nm and 3.25%with 538 nm,respectively.?2?.Four novel bi-donor unit TADF materials,2-t Bu Cz-?t Bu Czph Q?,3-t Bu Cz-?t Bu Czph Q?,3-PTZ-?PTZph Q?and 2-PTZ-?PTZph Q?,based on indole[2,3-b]quinoxaline as electron acceptor unit,phenothiazine and3,6-bis?tert-butyl?carbazole as electron donor unit,are designed and synthesized to investigate the influence of different donor units on their photophysical and electrochemical properties and electroluminescent performance.The results indicate that both materials show good thermal stability and blue-green emission in solution and solid film,respectively.In oxygen-free toluene solution,the delayed fluorescence lifetimes of 2-t Bu Cz?t Bu Czph Q?and 3-t Bu Cz-?t Bu Czph Q?are 1.1?s and 2.1?s,respectively.Based on PVK:OXD-7 as host materials and obtained materials as guest were fabricated with different dopant concentration,the 2-t Bu Cz-?t Bu Czph Q?-,3-t Bu Cz-?t Bu Czph Q?-,3-PTZ-?PTZph Q?-and 2-PTZ-?PTZph Q?-based devices exhibited a maximum external quantum efficiency(EQE_max)of 2.67%with a peak at508 nm,1.42%with 504 nm,6.75%with 597 nm and 5.49%with 594 nm,respectively.?3?.Two novel TADF materials,3-TPAQ and 2-TPAQ,based on indole[2,3-b]quinoxaline as electron acceptor unit,triarylamine as electron donor unit,are designed and synthesized to investigate the influence of different donor units on their photophysical and electrochemical properties and electroluminescent performance.The results indicate that both materials show blue-green emission in solution and solid film,respectively.Based on PVK:OXD-7 as co-host materials and obtained materials as guest were fabricated with different dopant concentration,the 3-TPAQ-and2-TPAQ-based devices showed a EQE_maxof 2.56%with a peak at 522 nm and 1.73%with a peak at 522 nm,respectively.