Design,Synthesis And Performance Of Boron/Selenium Multiple Resonance Organic Fluorescent Materials

Up to now,multiple resonance thermal activation delayed fluorescence(MRTADF)materials have achieved high efficiency and high color purity in vapor deposition devices.However,most MR-TADF materials have low reverse intersystem crossing rate constant and the molecular aggregation caused by their rigid planar structure can lead to spectral broadening and low efficiency.Therefore,this article aims to develop MR-TADF materials with high reverse intersystem crossing rate(kRISC)constant,and suppress aggregation by modifying the steric hindrance effect of functional groups,maintaining the narrow spectral luminescence characteristics of the material and improving luminescence efficiency.The specific research content is as follows:1.Three multiple resonance thermally activated delayed fluorescence dendrimers(BSeN-Cz,BSeN-DCz and BSeN-TCz)are developed by introducing the first-,secondand third-generation carbazole dendrons in periphery of boron,selenium and nitrogendoped polycyclic aromatic hydrocarbon(PAH)emitter for solution-processed narrowband blue organic light-emitting diodes(OLEDs).The dendrimers show rapid kRISC of 8.5 × 106 s-1,9.0 × 106 s-1 and 9.1 × 106 s-1,respectively,owing to the strong heavy-atom effect and spin-orbit coupling of selenium atoms.Meanwhile,intermolecular aggregation is effectively suppressed in the dendrimers owing to steric hindrance effect of carbazole dendrons,leading to nearly invariable narrowband emissions with full width at half-maximum(FWHM)kept at 32 nm at doping concentration up to 100 wt%for BSeN-TCz bearing third-generation carbazole dendron.Solution-processed OLEDs based on multiple resonance dendrimer BSeN-TCz(20 wt%)reveal blue electroluminescence at 478 nm with FWHM of 31 nm and Commission International de l’Eclairage coordinates of(0.11,0.21),together with maximum external quantum efficiency of 19.7%.2.Taking boron,selenium and oxygen doped polycyclic aromatic hydrocarbons as core,emitters for solution-processed narrowband blue organic light-emitting diodes(BSeO-UD1 and BSeO-UD2)were developed by introducing the steric group in periphery of selenium-doped polycyclic aromatic hydrocarbon.owing to the strong heavy-atom effect and spin-orbit coupling of selenium atoms,these emitters possess rapid reverse intersystem crossing rate constant of 3.5×106 s-1,3.7×106 s-1.Compared with the unprotected resonance skeleton BSeO,BSeO-UD2 with large steric hindrance structure is effectively wrapped,which can suppress the π-π interaction between molecules.Solution-processed OLEDs based on BSeO-UD2(10 wt%)reveal blue electroluminescence at 466 nm with FWHM of 49 nm and Commission International de l’Eclairage coordinates of(0.14,0.14),and the external quantum efficiency(EQE)of 20.2%.