Efficient red hybridized local and charge-transfer OLEDs by rational isomer engineering

Abstract

Developing highly efficient red emitters with emission beyond 600 nm is full of challenges for organic light-emitting diodes (OLEDs). Herein, two novel red isomers of 11-DTPA-BBI and 3-DTPA-BBI manifesting hybridized local and charge-transfer (HLCT) state were designed and synthesized, based on triphenylamine (TPA) as donor and 7H-benzo[de]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one (BBI) as acceptor. The charge-transfer (CT) component in HLCT state ensures their red emission and high excitons utilization, while the locally excited (LE) component guarantees the high fluorescence radiative rate. Further, the non-radiative transition is suppressed through regulating molecular vibration modes by isomer engineering, resulting in the high fluorescence quantum efficiency of 53% for 3-DTPA-BBI. Consequently, a maximum external quantum efficiency of 3.0% is achieved with emission peak at 604 nm in 3-DTPA-BBI based OLEDs. This contribution demonstrates a comprehensive structure-property relationship which may provide an effective guidance to design high performance red electroluminescent emitters.