Novel Red/Near-Infrared Delayed Fluorescence Materials:Synthesis,Mechanism And Application

Recently,organic light-emitting diodes（OLEDs）exhibit great potential to be the next-generation preoccupant display technology due to their unique role in the field of flat panel display.With the massive efforts from academia and industry,the manufacturing difficulty and production cost of OLEDs have been gradually reduced,making it popular in millions of households and everywhere.However,most commercial OLEDs remain expensive cost owing to noble-metal-containing materials,which hinders their further popularization and application,thus developing low-cost and easily available purely organic luminophores with high performance has become an inevitable trend.Since the concept of thermally activative delayed fluorescence（TADF）have been proposed in 2012,blue and green purely organic delayed fluorescence materials have been well developed in these years with maximum external quantum efficiencies(η_ext,maxs)over 40%of their OLEDs,exhibiting their huge potential in electroluminescence devices.Nonetheless,the performance of OLEDs based on red/near-infrared（Red/NIR）delayed fluorescence materials has lagged far behind by unfavorable factors,such as the energy gap law,aggregation-caused quenching and so on.Consequently,exploring the strategy of constructing Red/NIR delayed fluorescence materials with high performance is of great scientific and industrial significance for promoting the commercial production of purely organic Red/NIR OLEDs.Based on the background mentioned above,the research content of this paper is as follows:In chapter 2,we develop a series of novel aggregation-induced delayed fluorescence（AIDF）materials modified by long alkyl chains by endowing delayed fluorescence with aggregation-induced emission（AIE）property,and expect their high-performance solution-processed red OLEDs.All the luminophores realize high photoluminescence quantum yield in aggregate states and furtherly exciton utilization by suppressing exciton annihilation in the electroluminescence process.Moreover,the solubility and film-forming ability of these materials are effectively enhanced owing to the long arkyl chains.Their solution-processed orange OLED device attains theη_ext,maxof 14.7%with tiny efficiency roll-off of 6.1%at 1000cd m^?2,meanwhile the vacuum-deposited orange-red one furnishs theη_ext,maxof 14.1%with efficiency roll-off as low as 6.3%,indicating the great potential of AIDF materials in both solution-processed and vacuum-deposited high-effiency red OLED devices with low efficiency roll-off.In Chapter 3,a series of robust NIR TADF luminophores with intramolecular C?H···N hydrogen-bonding（H-bonding）interaction is constructed.High photoluminescence quantum yield and optical out-coupling factors are favored by introducing the intramolecular H-bonding without affecting TADF property.Their OLED devices emit withλ_ELs in the range of716?748 nm with high exciton utilization and the highestη_ext,max of 31.5%,which is the highest value among red OLEDs ever reported.These results suggest the construction of intramolecular H-bonding could be a practically useful approach for construsting robust NIR TADF materials.In Chapter 4,a series of highly efficient purely NIR TADF molecules is continuing developed.These molecules prefer significantly red-shift emission with maintained high photoluminescence quantum yield and enhanced optical out-coupling factors by extended conjugated moieties and intramolecular C?H···N H-bonding interaction.Meanwhile,the energy levels and orbital components in excited states are regulated through extending conjugated moieties,thus rapidly multi-channel reverse intersystem crossing process occurs.Their OLED devices exhibitλ_ELs in the range of 656?834 nm and provide the highestη_ext,maxof 31.0%.By introducing a red TADF sensitizer in Chapter 3,the sensitized OLED devices furnish a more outstandingη_ext,max of 32.9%,which is the highest value for deep-red OLEDs ever reported.According to the results,extending conjugated structures and introducing intramolecular H-bonding are effective for constructing high-performance purely NIR TADF materials.We hold a believe that more robust Red/NIR delayed fluorescence materials will be developed in the future,providing a boost to Red/NIR OLEDs and filling the blank space in the field of high-performance purely organic OLED by applying these strategies.