Design,Synthesis And Properties Research Of Red Fluorescent Materials Based On Bodipy

Organic light-emitting diodes（OLEDs）have broad application prospects in various fields due to its ultra-thin width,self-luminous,rich colors,wide selection of materials and flexible display.At present,the development of luminescent materials with high color purity has become current hot technologies,which was influenced by the demand for high color purity and high efficiency OLEDs.Until now,green and blue dyes with high color purity have been reported many times,but high-efficiency and narrow-spectrum red dyes are still relatively scarce,so it is of great significance to develop red dyes with high color purity for market demands.As we know,BODIPY is famous for its easy modification,narrow FWHM and high PLQY,which is an excellent basis for the preparation of red dyes.In this work,a series of narrow-spectrum red-emitting BODIPYs were developed by modifying different positions of the BODIPY,and the possibility of dendrimers being used for TADF sensitizer was verified in solution-processed devices.1.After changing the groups at theαandβ（1,7）positions of BODIPY derivatives and modifying the meso position with sterically hindered o-methoxybenzene units,three novel narrow-spectrum red materials were designed,synthesized and analyzed.Firstly,thermal decomposition temperature of Pht Bu OPh B,t Bu Ph OPh B and t Bu Nap OPh B are all greater than 300℃,which exhibit excellent thermal stability.The fluorescence spectra of the three BODIPYs are red-shifted sequentially,and the emission peaks in toluene solution are 607,615,and 624 nm,respectively.Secondly,a sterically hindered group was introduced at theβ（1,7）positions to limit the rotation of itself,which resulting in the narrow full width at half maxima（FWHM）for 35,41,and 41 nm.Thirdly,the contribution of theα-substituents to the molecular conjugation are greater than that of theβ（1,7）-substituents in the same case.After replacing the phenyl at theβ（1,7）positions of t Bu Ph OPh B with a naphthyl,the molecular conjugation can be further extended,so that the fluorescence spectrum is red-shifted and a narrow-spectrum red emission can be realized.Fourthly,in order to improve the color purity and efficiency of OLEDs,two dendritic TADF hosts were selected.The solution-processed OLEDs based on Pht Bu OPh B achieved the maximum brightness of 6512 cd m^-2,and the TSF-OLEDs based on t Bu Nap OPh B exhibit standard pure red emission with an EQE_max,an EL peak,a narrow FWHM,and CIE coordinates of 1.01%,632 nm,52 nm,and（0.67,0.33）,respectively.2.Two series novel molecules were designed and synthesized after changing the groups at the meso position of BODIPYs.Firstly,the change of the phenyl group to o-methoxybenzene can reduce the thermal decomposition temperature slightly,but the T_g of four BODIPYs are above330℃.Secondly,the modification of the larger sterically hindered group can increase the dihedral angle at the meso andβ（1,7）positions,which can make HOMO shallower（-3.351e V→-3.259 e V）while LUMO becomes shallower（-3.358 e V→-3.259 e V）,found by analyzed by t Bu Nap OPh B and t Bu Nap Ph B.However,the modification of the o-methoxybenzene unit at the meso position can only increase the dihedral angle at meso position and make the LUMO shallower（-3.400 e V→-3.411 e V）,which has basically no effect on the HOMO（-5.355 e V→-5.359 e V）due to its dihedral angle at theβ（1,7）positions found by analyzing 4OMe Ph B and 4OMe OPh B.Thirdly,the o-methoxybenzene unit can restrict the rotation of groups flanking the meso position and itself,which have opposite effects on the FWHM,but the stretching vibration of the carbon-oxygen bond will broaden the FWHM.The latter is dominant in results,and the substitution of phenyl to o-methoxybenzene unit will increase the FWHM by 2～5 nm.Among the four molecules,4OMe Ph B showed the most excellent performance with a PL peak of 634.4 nm and an FWHM of 35.6 nm.Fourthly,the solution-processed TSF-OLEDs based on Ph Cz-4Cz TPN/0.5%4OMe Ph B showed a EQE_max,FWHM and EL peak of 1.74%,50 nm and 634.4 nm,respectively.3.The synthesis and analysis of o OMe B and p OMe B were completed by changing theα-substituents of BODIPY derivatives.The results showes that p OMe B is better than o OMe B in terms of spectral wavelength,FWHM and efficiency.Firstly,the conjugation length of BODIPYs can be extended by connecting the methoxy group at the para-position of the phenyl units at theβ（1,7）positions,and the spectrum of p OMe B is red-shifted by 23.2 nm compared with o OMe B,showing positive red luminescence.Secondly,attaching the methoxy units at the ortho-position can not only increase the dihedral angle at theαpositions but also suppress the rotation of the o-methoxybenzene units.However,o OMe B loses more energy through vibrational transitions,reflecting the more vigorous vibration of the o-methoxybenzene units indicated by stokes shift,which leads to the narrower FWHM of p OMe B.Thirdly,the solution-processed OLEDs based on p OMe B were superior to o OMe B in terms of turn-on voltage,brightness,color purity,and EQE_max,and the device based on Ph Cz-4Cz TPN/1.0%p OMe B emitters achieved standard red emission with turn-on voltage,EL peak,EQE_max,and CIE coordinates of 4.1V,644 nm,1.27%and（0.67,0.33）,respectively.