Multiple resonance thermally activated delayed fluorescence dendrimers containing selenium-doped polycyclic aromatic hydrocarbon emitters for solution-processed narrowband blue OLEDs

Three multiple resonance thermally activated delayed fluorescence dendrimers (BSeN-Cz, BSeN-DCz and BSeN-TCz) are developed by introducing the first-, second- and third-generation carbazole dendrons in periphery of selenium-doped polycyclic aromatic hydrocarbon emitter for solution-processed narrowband blue organic light-emitting diodes (OLEDs). It is found that the dendrimers show strong thermally activated delayed fluorescence effect with rapid reverse intersystem crossing rate constant of 8.5–9.1 × 106 s−1 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) reveal blue electroluminescence at 478 nm with FWHM of 31 nm and Commission International de 1′Eclairage coordinates of (0.11, 0.21), together with maximum external quantum efficiency of 19.7%, which is promising device efficiency for narrowband blue electroluminescence by solution process.