1.42-Fold Enhancement of Blue OLED Device Performance by Simply Changing Alkyl Groups on the Acridine Ring

Developing high-efficiency blue thermally activated delayed fluorescence (TADF) emitters is still a formidable challenge. Here, we report five blue TADF emitters designed by simply changing the frequently used methyl group (C1) to a longer one gradually to subtly adjust the energy levels. DAc-C1–DAc-C5 are developed by using diphenylsulfone (DPS) as the acceptor and acridine with different-length alkyl chains on C(9) as the donor groups. These five compounds have high photoluminescence quantum yields (PLQYs) (75%–84%) with blue emission. The DAc-C2-based OLED device exhibits the maximum external quantum efficiency (EQE) of up to 24.1% with CIE (0.15, 0.19), which is 1.42 times higher than that of state-of-the-art TADF OLEDs based on DAc-C1 (EQE: 17.0%) under the same conditions, confirming the power of the molecular design strategy. Furthermore, the crystal analyses partially explain the influence of the alkyl chain on the device property, demonstrating a new approach for achieving TADF luminogens with high performance.