Design,Synthesis And Photoelectric Properties Of Narrow-band Luminescent Materials Based On Boron-oxygen Framework

Organic Light-Emitting Diodes(OLEDs),as the latest generation of display and lighting technology,possess unique advantages such as flexibility,lightweight,vibrant colors,and high contrast.Although commercial OLED products with full-color and dynamic displays have become widespread,they still face various technical challenges.One of the central challenges is the lack of high-quality blue light-emitting materials,particularly pure organic molecules that are not heavy-metal complexes.While optimizing device fabrication processes or employing other techniques can enhance and control the existing blue light quality to some extent,the fundamental and efficient solution lies in the development of crucial blue-light materials that meet current high-end display requirements.In recent years,the thermally activated delayed fluorescence(TADF)emission material system under the multiple resonance(MR)effect has gradually emerged as a favorable complement and extension to existing commercial luminescent systems.This system,characterized by strong planar rigidity and easy structural design,exhibits unique advantages such as narrow spectral emission,high color purity,and high performance.The further improvement and development of this system are crucial for the future direction of the OLED industry.While boron-oxygen full-color light materials are commonly reported and have achieved excellent efficient narrow-band emission,the current mainstream MR-TADF system mostly relies on materials based on boron-nitrogen core structures,demonstrating outstanding narrow-spectrum emission.Nevertheless,the boron-oxygen system,especially in the short-wavelength and deep-blue light material system,possesses inherent advantages in natural intrinsic luminescence.Additionally,compared to other multiple resonance core structures,it offers more rich modification sites for controlling molecular excited states.Boron-oxygen systems,which combine weak acceptors with multiple resonance properties,provide a more flexible design strategy and maintain the highest record of blue light color purity.However,the discussion on the design strategy of narrow-band boron-oxygen materials is somewhat limited,mostly focusing on a purely donor-acceptor perspective using conventional TADF material molecular design strategies.To delve into the design of boron-oxygen materials and their modulation strategies under the multiple resonance effect,this study focuses on the boron-oxygen core framework.Through rational molecular design modifications,a series of short-wavelength narrow-band multiple resonance materials are constructed.The research is outlined as follows:In Chapter 2,a pair of isomeric violet light molecules,SF1 and SF2,was constructed by connecting the weak donor unit tert-butyl carbazole to the boron-oxygen core through two ends of spirofluorene.The weak intramolecular charge transfer characteristics between the donor and acceptor resulted in a slight redshift in the emission spectra relative to the violet boron-oxygen core.For the doping devices based on the emissive molecule SF1,the emission peak was at 432 nm,with CIE coordinates(0.155,0.048),achieving a maximum external quantum efficiency(EQE)of 4.24%.For the device based on the molecule SF2 with TADF properties,the emission peak was at 416 nm,with CIE coordinates(0.14,0.026),achieving a maximum EQE of 4.44%.Due to the more twisted rigid structure and weaker charge transfer state of SF2,it achieved narrower violet light emission and a smaller coordinate y value.In Chapter 3,two deep-blue light molecules,OA and SA,were constructed by directly connecting the boron-oxygen core with the oxygen-sulfur-fused spiropyridine donor through the classical direct linkage method.Due to the overall twisted structure of the molecules inducing a greater degree of orbital separation,the molecules exhibited a very small(less than 0.05 e V)singlet-triplet energy level difference.Theoretical analysis indicated that the molecules maintained the multiple resonance effect of the boron-oxygen core structure,contributing to the narrowing and promoting delayed fluorescence.Therefore,under the control of a strong long-range charge transfer state,both molecules still achieved narrow-spectrum deep-blue light emission.Based on OA,the doping device of the emissive molecule achieved a maximum external quantum efficiency of 11.6% at CIE coordinates(0.143,0.095),while the device based on SA reached a maximum external quantum efficiency of11.4% at CIE coordinates(0.142,0.113).Both maintained low efficiency roll-off,attributed to their short delayed fluorescence lifetimes.In Chapter 4,blue-light boron-oxygen materials DTP and DPC,with further enhanced intramolecular charge transfer states,were obtained by connecting triphenylamine and phenylcarbazole,respectively,to the boron-oxygen symmetric positions.Due to the use of a more rigid donor,DPC exhibited a greater degree of blue shift and spectral narrowing compared to DTP.Theoretical calculations and photophysical tests showed that DPC had a stronger intramolecular multiple resonance effect,accelerating reverse intersystem crossing,and a shorter delayed fluorescence lifetime.Based on DTP,the doping device of the emissive molecule achieved a maximum external quantum efficiency of 28.2% at a blue shift to 476 nm and CIE coordinates(0.141,0.254),while the device based on DPC reached a higher efficiency of 38.6% at a blue shift to 464 nm and CIE coordinates(0.142,0.152),placing it at the highest efficiency level among non-sensitized devices for blue-light boron-oxygen materials.