Multiple Resonance Organoboron OLED Emitters with High Efficiency and High Color Purity via Managing Long- and Short-Range Charge-Transfer Excitations

Multiple resonance (MR) type thermally activated delayed fluorescence (TADF) emitters are very promising in the high-resolution and high-efficiency displays, due to their narrow and highly efficient optical emissions. Early MR-TADF cores that show only short-range charge-transfer (CT) electronic excitations hardly afford ideal performances (e.g., show low efficiencies) in organic light-emitting diodes (OLEDs). This work thus designs and synthesizes two MR-TADF emitters (TCzBN-BP and TCzBN-FP), where the same MR core TCzBN is chemically modified by the acceptor fragments benzophenone/9-fluorenone (BP/FP) to incorporate long-range CT excitations in the two molecules. OLEDs exploiting TCzBN-BP as emitter, in which short-range CT excitation is dominant in the first singlet (S₁) excited state, achieve a maximum external quantum efficiency (EQE) of 35.6% and a narrow emission bandwidth of 35 nm. In contrast, OLEDs exploiting TCzBN-FP with an overloaded long-range CT excitation in the S₁ state exhibit a maximum EQE of 27.2% and a broadened emission bandwidth of 56 nm. This work not only shows the importance of careful management of long- and short-range CT excitations, but also provides a new insight into the structure–property relationship in the MR-TADF emitters, which thus promotes the design of more novel MR-TADF emitters with high efficiencies and high color purity. © 2023 Wiley-VCH GmbH. © 2023 Wiley-VCH GmbH