Efficient orange-red thermally activated delayed fluorescence material containing a cyano group

The development of efficient long-wavelength TADF emitters has been full of challenges owing to the various strict molecular design limiting factors. Herein, two orange-red TADF emitters, namely 3DMAC-BP-Br and 3DMAC-BP-CN, based on donor 9,9-dimethyl-9,10-dihydroacridine (DMAC) and rigid acceptor dibenzo[a,c]phenazine (BP) modified by electron-withdrawing bromine atom or cyano group, were designed and synthesized. Both emitters have large twisted D-A-D structure. The strong electron-withdrawing capabilities of the bromine atom or cyano group can dramatically affect photoelectric properties of the emitters by enhancing the intramolecular charge transfer (ICT) effect and enlarge conjugation with the BP group. Hence, both emitters have high PLQY values (83% and 92%, respectively) in doped films and possess simultaneously small ΔE_ST values (0.04 and 0.02 eV, respectively). As a result, both 3DMAC-BP-Br and 3DMAC-BP-CN show superior device performance. Especially, DMAC-BP-CN based OLED exhibits a maximum external quantum efficiency (EQE) of 22.43% and low turn-on voltage of 2.8 V.