Design,Synthesis And Characterization Of High-Performance Deep-Red/Near-Infrared Thermally Activated Delayed Fluorescent Materials Based On Acenaphtho[1,2-b]pyrazine Derivatives

Since C.W.Tang invented the double-layer structure,organic electroluminescence devices have made considerable progress in the visible-light region and they have been widely used in panel display,solid-state lighting and so on.Comparatively speaking,the development of deep red,especially near-infrared?NIR?luminescent materials lags behind relatively.However,deep-red/NIR luminescent materials play an irreplaceable role in such emerging fields as night vision,information security,and optical communications.Therefore,in recent years,the development of newly efficient deep-red/NIR luminescent materials has become a research hotspot and difficulty in the field of organic optoelectronics.To date,the organic emitters suitable for deep-red/NIR electroluminescent devices mainly include donor-acceptor type fluorescent small molecules and transition metal complexes.Unfortunately,their mass production is restricted by exciton utilization and the cost,respectively.In 2009,Professor Adachi proposed thermally activated delayed fluorescence?TADF?materials without noble metal.TADF materials have a small energy gap(?E_ST)between the lowest singlet and triplet excited state so that the generated triplet excitons can be back to singlet state through the reverse intersystem crossing,thereby achieving 100%exciton utilization.Therefore,TADF is regarded as an ideal alternative for phosphorescence and conventional fluorescence,and it is expected to obtain effective deep red/near-infrared luminescent materials with practical application value.In this dissertation,a series of highly efficient deep-red/NIR TADF materials were obtained by derivatization of dicyano-substituted acenaphtho[1,2-b]pyrazine moieties,and their thermal stability,photophysical properties,and electroluminescence properties were studied systematically to reveal the relationship between different derivatization methods and material properties.1.In the second chapter,we designed a new acenaphtho[1,2-b]pyrazine-based electron-withdrawing groups,APDC,and then TADF material APDC-DTPA was synthesized by introducing two diphenylamine as electron-donating groups at APDC's3rd and 4th positions and a benzene as connecting bridge.Due to the presence of a strong intramolecular charge transfer state,there is deep-red/NIR emission upon excitation.Meanwhile,due to the moderate overlap of HOMO/LUMO,APDC-DTPA has a high fluorescence quantum yield and excellent performance in the corresponding devices.2.In Chapter 3,we studied the effect of isomeric phenomena on the performance of materials and devices.The isomeric APDC-o DTPA of APDC-DTPA was obtained by derivatization at positions 2 and 3 of APDC.The experimental results show that the performance of ortho-connected materials based device is close to that of AODC-DTPA,but the spectrum shows an obvious blue shift.3.In Chapter 4,we explored the effects of increasing donor electron-donation capability on materials and device performance.APDC-DMPA and APDC-DOPA were obtained by replacing the electron-donating groups of APDC-DTPA with 4,4'-dimethyldiphenylamine and 4,4'-dimethyldiphenylamine respectively.The experimental results show that due to the increase in electron-donating ability of the donors,their spectra have a large red shift compared with APDC-DTPA,and the spectra in the neat film reach the real NIR region.At the same time,devices based on these two materials also exhibit superior device performances.4.In Chapter 5,in order to obtain a true NIR TADF material,we replaced the donor group with phenoxazine and 9,10-dihydroacridine derivatives,which possess rigid structure and strong electron-donating ability,obtaining APDC-DAdP and APDC-DPz P.The experimental results show that both materials have TADF properties,and the emission peaks are substantially redshifted from that of APDC-DTPA.At the same time,due to the increase in the rigidity of the donor groups,energy loss caused by vibration and rotation of the molecules can be effectively reduced,so that devices based on both materials exhibit excellent performance as well.5.In Chapter 6,we explored the effect of increasing the conjugation length of the donor on the material and device performance.A new electron-withdrawing group,acenaphtho[1,2-b]quinoxaline?AQDC?,was obtained by incorporating a benzene ring on APDC.Similarly,the electron-donating group was introduced into the benzene ring at the 3rd and 4th positions of AQDC,obtaining new TADF materials AQDC-DTPA and AQDC-DMPA.The experimental results show that the spectrum is significantly blue shifted compared to APDC-DTPA due to the introduction of benzene ring,which increases the distance between the nitrile group and the donor.However,due to the introduction of a benzene ring,the fluorescence quantum yield of the material is increased,and therefore,the AQDC-DTPA-based device exhibits particularly excellent performance.7.In the seventh chapter,we designed two D-?-A deep-red/NIR materials APDC-TPA and APDC-PTPA in view of the problems of the D-?-A-?-D materials in the previous chapters,and the effect of different?bridge lengths on material properties was studied.The experimental results show that the D-?-A materials of this series also have TADF properties,and the steric hindrance between benzene bridges and APDC is reduced,so that these materials have a higher quantum yield compared with APDC-DTPA.More importantly,adding one more benzene bridge can effectively reduce the?E_STof the material.Therefore,APDC-PTPA-based devices have more excellent device performance.