Polynorbornene-Based Blue-Emitting Fluorescent Polymers:Design,Synthesis And Performance

Blue polymer emitters have been emerged as crucial alternatives in RGBs materials for developing solution-processed organic electroluminescent devices.However,the inferior electroluminescence efficiency and poor color purity inevitably hinder their commercial application in full-color display and white lighting.Consequently,aiming to developing efficient blue polymer emitters,we employ polynorbornene scaffold to confine electron donor and electron acceptor with spatial proximity,wherein through-space charge transfer(TSCT)and efficient thermally activated delayed fluorescence(TADF)effect can occur to boost up the exciton utilization,and thus the resulting TSCT-polymers demonstrate efficient electroluminescence with blue emission.Furthermore,we have synthesized a series of polynorbornene polymer hosts with high triplet level,and simultaneously developed novel boron/sulfur(selenium)/nitrogen doped multiple resonance emitters for narrowband blue emission.Finally,by doping narrowband blue emitters in polymer hosts as emissive layers,solution-processed OLEDs with high color purity have been assembled.1.By using polynorbornene as the non-conjugated backbone,while combining donors with different topological structures(acridan or dendritic teracridan)and 1,3,5triphenyl-triazine as acceptor,through-space charge transfer polynorbornenes with fixed and controllable spatial alignment of donor and acceptor are reported for blue emission.Compared to edge-to-face alignment between donor and acceptor,face-toface aligned mode are more prone to increase spatial D-A interactions,which exhibit reasonably larger oscillator strength and promising PLQY up to 74%,accompany with a high reverse intersystem crossing rate of 5.9×l06 s-1。As a result,solution-processed OLEDs based on TSCT polynorbornenes bearing teracridan as donor and 1,3,5triphenyl-triazine as acceptor reveal blue emission at 479 nm,as well as CIE coordinates of(0.21,0.29),corresponding to a high maximum external quantum efficiency of 18.8%.2.By using polybenzonorbornene as the non-conjugated backbone,while attaching carbazole/3,6-di-tertbutylcarbazole donors and triphenylboron acceptor to ortho position of the benzene bridge to simultaneously endow face-to-face D-A alignment for through-space CT interactions and π-bridge-mediated through-bond CT interactions,a series of polybenzonorbornenes combining through-space and throughbond CT effect are developed for blue emission.As expected,the through-space D-A interactions is beneficial to obtain effectively separated HOMO/LUMO distribution and thus enabling small ΔEST(0.15-0.18 eV),Meanwhile,the incorporation of throughbond interactions is favorable for enhancing the oscillator strengths and radiative decay rates of 2.3-2.5×107 s-1.As a result,solution-processed OLEDs based on polybenzonorbornenes bearing 3,6-di-tertbutylcarbazole as donor and triphenylboron as acceptor reveals blue electroluminescence with peak at 472 nm and CIE coordinates of(0.15,0.23),as well as maximum external quantum efficiency of 9.5%.3.By using non-conjugated polynorbornene as backbone and incorporating different hole transport units(carbazole,acridine and second-generation acridine)as pendant in side chain,we have developed a series of polynorbornene hosts with high triplet energy(ET)and well hole transport ability.Owing to the non-conjugated backbone,high ET of 3.12-3.20 eV for hosts are obtained to suppressed the energy back-transfer of triplet for blue/deep blue emitters.Meanwhile,as the pendants changes from carbazole to acridine and dendritic teracridan,the shallower HOMO levels are observed from-5.5 0 e V to-5.23 eV and-5.11 eV,which could facilitate hole inj ection.Meanwhile,by employing boron as electron-deficient atoms and sulfur(selenium)and nitrogen as electron-rich atoms,a series of boron/sulfur(selenium)/nitrogen-doped multiple resonance emitters featuring single-boron or double-boron based polycyclic frameworks have been developed for narrowband blue emission.The resulting emitters exhibit narrowband blue emission with peak at 463-479 nm and full width at halfmaximum(FWHM)of 16-30 nm,as well as promising PLQY of 82-95%.Moreover,rapid reverse intersystem crossing rate of 7.5-8.8×106 s-1 are achieved in seleniumdoped emitters.Finally,solution-processed OLEDs assembled with polynorbornene polymer as host material and boron/selenium/nitrogen-doped multiple resonance blue emitters as dopants revealed ultrapure blue electroluminescence with peak at 472 nm and FWHM of 30 nm leading to CIE coordinates of(0.13,0.20),corresponding to a high maximum external quantum efficiency of 20.2%.