Anthracene-Based Blue Fluorescent Materials:Molecule Engineering And Applications In High-Efficiency Non-doped Organic Light Emitting Devices

Organic light emitting diodes（OLEDs）have attracted much attention in flat panel displaying and full-colour lighting fields due to their flexibility,light weight and low cost.As one of the pure primary full colours（red,green and blue）,blue light emitting materials are indispensable in OLEDs because it can not only be used as blue emitters but also generate green and red light by energy transfer in white OLEDs.However,it is an important challenge to obtain high efficiency deep-blue emitters due to intrinsically wide energy band gap,resulting in unbalanced carrier transmission and low external quantum efficiency（EQE）of the device.In order to solve this problem,blue lighting molecules with narrow bandgap based on anthracene were designed and synthesized by adjusting the linkages between donor and acceptor.Their photophysical properties,the natures of excited state and performances in non-doped blue OLEDs were investigated in detail.The main research contents are as follows:To state the effect of peripheral groups on photophysical in anthracene-base materials,four emitters were designed and sysnthesized using 1,2-diphenyl-1H-phenanthro[9,10-d]imidazole（PPI）as chromophore unit,anthracene as bridged unit and 1-naphthyl,2-naphthyl,benzene and phenylcarbazole as peripheral groups,namely PPIAn1N,PPIAn2N,PPIAnp and PPIAnCz.The results indicated that four molecules all exhibited hybridized local and charge transfer（HLCT）excited states with dominated locally excited（LE）state due to the PPI unit.The maximum emission peaks of four molecules in the films are 433,448,446 and 450 nm,respectively,which are located in the range of blue light emission.By introducing peripheral groups,the conjugated structure of the material is extended,the aggregation modes of molecules are changed,the PL spectra exhibited a tiny red shift.Energy gap of T₂ and S₁ of the material is reduced,and the gap of T₂and T₁ of the material is increased,the triplet excitons from T₂can be converted into singlet excitons by reverse intersystem crossing（RISC）.The non-doped device based on PPIAn2N displayed the better performance with maximum emission peak at 452 nm,the color coordinate（Commission International de L′Eclairage,CIE）of（0.15,0.11）,the maximum power efficiency（PE）of 6.3 lm/W and the maximum EQE of 7.3%was achieved.In order to obtain deep-blue light emitting material with narrow bandgap,three molecules of pCzAnN,mCzAnN and 3CzAnN were designed and synthesized by introducing phenylcarbazole as the donor,anthracene as acceptor and the 2-naphthyl group as the peripheral group.The molecular structure of mCzAnN is relatively distorted,because the conjugated structure is interrupted,RISC of triplet excitons can not be realized,mCzAnN is a traditional fluorescent material,while pCzAnN and 3CzAnN exhibit exhibited HLCT excited states with dominated LE state.The maximum emission peaks of three molecules in the films are 442,440 and 449 nm,respectively,which are located in tha range of blue light emission.For pCzAnN and 3CzAnN,the energy gap of T₂ and S₁ is small,the triplet excitons from T₂can be converted into singlet excitons by RISC.The non-doped device based on pCzAnN displayed the better performance with maximum emission peak at 444 nm,the CIE of（0.15,0.07）,PE_max of 2.7 lm/W and the maximum EQE of 6.0%were achieved.