Tuning the emission from local excited-state to charge-transfer state transition in quinoxaline-based butterfly-shaped molecules: Efficient orange OLEDs based on thermally activated delayed fluorescence emitter

We designed and synthesized a series of new butterfly-shaped D-A-D type compounds with quinoxaline as an electron acceptor. Their photoluminescence (PL) spectra are successfully tuned from green to orange based on the intramolecular charge transfer effect. Moreover, through theoretical and experimental approaches, we have verified the dihedral angles between the donor and acceptor, the value of Delta E-ST and the nature of T-1 play crucial roles in shaping the emissive properties, and we have also successfully tuned the emission type from local excited-state (LE) to charge-transfer state (CT) transition to acquire a TADF molecule. A high rate constant for reverse intersystem crossing (RISC) is up to 1.5 x 10(6) s(-1). The BDQDMAC-based orange TADF OLEDs exhibit a maximum external quantum efficiency of 7.4%, corresponding to a prominent contribution of 97% from the delayed fluorescence to the overall external quantum efficiency. (C) 2017 Elsevier Ltd. All rights reserved.