The Synthesis And Photoelectric Properties Of Polyfluorene Blue Materials Based On New Chromophores

Polymer Light-Emitting Diode(PLED)has the advantages of solution processing,low cost,and large area preparation,and be well used in large-area flexible display and solid-state lighting equipment.Therefore,PLED has great commercial application potential.As the indispensable component for full-color display,the blue light-emitting polymers used in PLEDs are usually polyfluorene derivatives.However,the electroluminescence efficiency of most blue polyfluorene derivatives is less than 3 cd A^-1,luminescence spectrum is instability,and the lifetime is short,therefore the application of PLED is still limited.In this paper,a new type of chromophore unit is designed and synthesized and introduced into the polyfluorene main chain,which improves the carrier injection of the PLED device and balances the carrier transmission,thereby improving the luminous efficiency of the blue PLED device,lifetime and other performance,the work carried out is as follows:(1)In the second chapter,a phenoxazine(PO)unit with high hole mobility and high fluorescence quantum yield was synthesized and introduced into the polyfluorene backbone to obtain polymers PF-PO1,PF-PO2 and PF-TD2PO1.This series of polymers all have better thermal stability,higher fluorescence quantum yield and more suitable energy levels.Among them,the maximum luminous efficiency of the single-layer device and the double-layer device based on the polymer PF-TD2PO1 are 3.07 cd A^-1 and 5.18 cd A^-1,respectively,and it is a deep blue emitting device with a color coordinate of(0.15,0.11).Subsequently,the introduction of hole-transporting small molecule BCFN into the double-layer device based on polymer PF-TD2PO1 further improved the hole-transporting ability of the device and balanced the hole and electron carrier transport in the device.After optimization,the starting voltage of the device is3.0 V,the maximum luminous efficiency is 6.20 cd A^-1,the maximum luminous brightness is44685 cd m^-2,the color coordinate is(0.15,0.11),and the lifetime T₆₀ of the device exceeds 16hours.(2)In Chapter 3,a seven-membered fused-ring conjugated unit(DFSO)was synthesized based on the Dibenzothiophene-S,S-dioxide(SO)unit and the fluorene ring at its two ends.By broadening the conjugate plane of the chromophore,the DFSO unit has a higher fluorescence quantum yield than the PO unit.The DFSO unit was introduced as a chromophore unit into the polyfluorene backbone to synthesize polymers PF-DFSO5,PF-DFSO10,PF-DFSO15 and PF-DFSO20.Among them,the double-layer device based on polymer PF-DFSO5has a maximum luminous efficiency of 3.71 cd A^-1,a maximum brightness of 16566 cd m^-2,and a CIE color coordinate of(0.18,0.13).It is a high-efficiency blue light device.In addition,as the content of DFSO units in the polymer increases,the polymer is more likely to produce exciplexes in the aggregated state,thereby generating new excited states and gradually increasing the emission at 556 nm.Among them,the device based on polymer PF-DFSO20 has a maximum luminous efficiency of 7.98 cd A^-1,a color coordinate of(0.30,0.32),and a color rendering index of 78.It is a single-component high-efficiency white light device.