Design Synthesis And Photoelectric Properties Of Organic Blue Molecule Based On Benzoxazole As Acceptors

Organic light-emitting diodes（OLEDs）,as a new generation of display technology,are gradually surpassing liquid crystal displays in the field of high-end displays.One of the key factors restricting the development of OLED is the lack of high-performance blue light materials.Although blue phosphorescent materials and thermally activated delayed fluorescent materials have achieved great breakthroughs in device efficiency,there are still great challenges in the development of pure blue and deep blue materials,and the stability of the devices is related to actual industrial applications.There is still a big gap.At present,blue light materials with excellent comprehensive performance are mostly concentrated in D-π-A blue light molecules with large conjugated groups such as anthracene or fluorene as conjugate bridges.Such molecules are characterized by large planar conjugate bridges and twisted structures.The introduction of acceptor groups gives the material high fluorescence efficiency and carrier balance characteristics.However,this type of molecular structure is relatively complex,single structure,and limited in variety.Therefore,there is an urgent need to develop new organic blue molecules and high-performance blue light.OLED device.In this article,we chose benzoxazole as the acceptor,and constructed a new type of DA molecule with a simple structure through the bonding of donors of different strengths and structures,and performed various performance characterizations.To explore the potential of benzoxazole as a blue light chromophore,Details as follows:（1）The target molecules PCZPBO and TPAPBO were synthesized using common donor groups phenylcarbazole and triphenylamine as donors and benzoxazole as acceptors.Both structures are distorted to a certain degree.The solvation model of the two molecules is analyzed,and there is a hybrid local and charge transfer（HLCT）state in the molecules,which is conformed with theoretical calculations.Electroluminescence devices were prepared by using the two as the light-emitting layer.The electroluminescence peak positions of both were in the blue range.PCZPBO exhibited a dark blue luminescence,which electroluminescence peak position at 412 nm,CIE color coordinates（0.15,0.07）,The maximum external quantum efficiency is 5.1%;the electroluminescence peak of TPAPBO is at 452 nm,the CIE color coordinates（0.15,0.15）,and the maximum external quantum efficiency is 4.3%.Both showed good device performance,which proved the success of molecular design,but there is no major breakthrough has been made in the external quantum efficiency of device,so further optimization of the molecular structure is required.（2）Two target molecules,PPIPBO and 4-PCZPBO,were synthesized using phenanthrimidazole and 3-bromo-9-phenyl-9H-carbazole as donors and benzoxazole as acceptors.The properties of the material were characterized,and both molecules showed stable thermal and electrochemical properties.The photoluminescence spectra of them were tested,and the emission wavelengths were all in the blue range.The non-doped electroluminescent device prepared with the two as the light-emitting layer showed excellent performance,and the device with 4-PCZPBO as the light-emitting layer showed pure blue emission.The CIE coordinates are（0.15,0.13）,and the maximum EQE is 6.0%;The device with PPIBPO as the light-emitting layer exhibits blue light emission,the CIE coordinates are（0.17,0.30）,the maximum EQE is 6.6%,and the efficiency roll-offs of the two devices are 5.0%（4-PCZPBO）and 0.5%,respectively（PPIPBO）,the calculated exciton utilization rates are 33.5%（4-PCZPBO）and 40.9%（PPIPBO）,respectively.Further analysis of the exciton utilization rate exceeding the 25%exciton spin statistical limit,the excited state of the material is the HLCT state,and the thermal exciton channel may be opened between the S₁state and the high-level triplet state,making the triplet excitons in The high energy level is converted into singlet excitons,thereby achieving high exciton utilization.These works illustrate the success of molecular regulation by regulating donors,pave the way for future work on the same system,and further prove the potential and use value of benzoxazole groups as blue light chromophores.