Designing dual emitting cores for highly efficient thermally activated delayed fluorescent emitters

Improving the efficiency and the stability of TADF-based OLED devices is of vital importance for OLED applications. In this work, two dual emitting cores (2,2′-DPXZ-PN and 3,3′-DPXZ-PN) were rationally synthesized by connecting two identical TADF emitting units and were confirmed with obvious TADF features. The thermal stability accompanied by high T_d, T_g and T_m values was obtained via the design of an extension of the molecular structure. Meanwhile, the molar extinction coefficients and PLQYs of the two dual emitting cores were also dramatically improved, of which 3,3′-DPXZ-PN in 10 wt% doped CBP film resulted in a PLQY as high as 82%. Based on the high PLQY values and TADF features, maximum external quantum efficiency (EQE) values of 13.4% for a 2,2′-DPXZ-PN-based OLED device and 14.9% for a 3,3′-DPXZ-PN-based OLED device were achieved with a slow efficiency roll-off of 12% and 13.5% at a high luminance of 1000 cd m^-2.