Synthesis And Opetoelectronic Performances Of Dibenzothiophene-S,S-Dioxide-Based Fused-Ring Unit And Polymers

Polymer light-emitting diodes（PLEDs）have great application potential in flexible display and solid-state lighting due to their solution-processed procedure,low-cost and easy to large-area manufacturing.Among the red,green and blue light-emitting polymers,efficient and stable blue light-emitting polymers is still one of the key issues that restricts the commercial application of PLEDs.The HOMO and LUMO levels of the wide band-gap blue-emitting polymers are difficult to match with the energy levels of the carrier injection/transport layers.Thereinto,the banlanced of carrier injection and transportation is an important factor that affects the efficiency of blue light-emitting polymers.Dibenzothiophene-S,S-dioxide（SO）has high fluorescence quantum yields,good chemical and thermal stability.The strong electron affinity of SO is beneficial to the electron injection/transportation.The five rings fused compounds（BTOF/BTOCz）based on SO have larger conjugate plane and space for structural adjustment.The LUMO and HOMO levels of polymers are easy to adjust,which can promote the balance of carrier injection and transport,improving the efficiency and stability of devices.1)BTOF is an electron-withdrawing moiety,which shows good solubility and high fluorescence quantum yields.PF-BTOFs and PCz-BTOFs were synthesized via introducing BTOF into the polyfluorene（PF）and polycarbazole（PCz）backbone,respectively.The introduction of BTOF reduced the lowest unoccupied molecular orbital（LUMO）energy levels of polymers and the electron injection barrier of device,promoted the balance of carrier injection/transport.PF-BTOF30 exhibited the maxmium luminous efficiency(LE_max)of 3.7 cd A^-1 with the CIE coordinates of（0.16,0.17）in a single-layer device.2)BTOCz shows a bipolar charge-transport characteristic.PF-BTOCzs and PCz-BTOCzs were synthesized via introducing BTOCz into the PF and PCz backbone,respectively.The introduction of BTOCz facilitated the balance of carrier injection/transportation.PF-BTOCz30and PCz-BTOCz30 exhibited the LE_max of 6.26 cd A^-1 and 6.06 cd A^-1 with the CIE coordinates of（0.16,0.21）and（0.17,0.26）in a single-layer device,respectively.3)BTOCz is a linear coplanar structure,while the isomer（i-BTOCz）is a twisted coplanar structure.PF-i-BTOCzs and PCz-i-BTOCzs were synthesized via introducing i-BTOCz into the PF and PCz backbone,respectively.The twisted structure of i-BTOCz disturbed the effective conjugation length of polymers and resulted in blue-shift of spectra.With the increasing content of i-BTOCz unit,the electroluminescent（EL）spectra and color coordinate of the device based on blue light-emitting copolymers changed slightly.4)PPF-NSs were synthesized via introducing the electron-donor unit（NS）into the PF backbone.When the content of NS was 1%,the EL spectra of polymers was blue emission.With the content of NS reached 3%,the EL spectra of polymers shown red-shift with blue-green/green emission.A LE_max of 3.05 cd A^-1 with the CIE coordinates of（0.17,0.20）was obtained from PPF-NS1 in a single-layer device.PPF-NS10 exhibited a LE_max of 7.20 cd A^-1with the CIE coordinate of（0.25,0.55）in a sigle-layer device.5)The electron-acceptor unit（NSO）has strong rigid and high fluorescence quantum yields.PPF-NSOs were synthesized via incorporating NSO unit into the PF backbone,which was beneficial to improve the electron injection/transportation ability.There was blue emission with the content of NSO not exceeded 3%.When the content of NSO exceeded 3%,polymers exhibited the bluish green emission.PPF-NSO3 and PPF-NSO10 exhibited a LE_max of 5.22 cd A^-1 and 6.73 cd A^-1 with the CIE coordinates of（0.15,0.24）and（0.17,0.34）in a single-layer device,respectively.PCz-NSOs were synthesized via introducing NSO into the PCz backbone,which shown green emission.PCz-NSO30 exhibited the LE_max of 5.65 cd A^-1 with the CIE coordinates of（0.27,0.53）in a single-layer device.