Regulating the optoelectronic properties of red TADF emitters based on an acenaphthylene-1,2-dione through electron-donating engineering†

Currently, red light-emitting materials with thermally activated delayed fluorescence (TADF) properties exhibit significant potential for application in organic light-emitting diodes (OLEDs), however, their wide applications are limited by the energy gap law. In this work, a weak electron-withdrawing moiety acenaphthene 1,2-dione (ADO) was selected, and it was functionalized with different electron-donating (D) units, such as triphenylamine (TPA), naphthylphenylamine (NPA) and biphenylphenylamine (BBPA), for the construction of D–A–D-type red TADF emitters, namely, ADO-DTPA, ADO-DNPA and ADO-DBBPA. Results indicated that the pure films of these materials exhibited an intense red emission exceeding 690 nm and possessed TADF properties. In particular, owing to the strongest electron-donating capability of the BBPA unit among the three electron-donating units, ADO-DBBPA exhibited a superior photoluminescence quantum yield (PLQY) of 10.15%, a minimal energy gap (ΔE_ST, 0.11 eV), an elevated effective reverse intersystem crossing rate (RISC, k_RISC: 5.89 × 10³ s⁻¹), and an outstanding electroluminescent performance (λ_EL = 626 nm, EQE_max = 1.479%) compared to the ADO-DTPA (λ_EL = 618 nm, EQE_max = 1.324%) and ADO-DNPA (λ_EL = 624 nm, EQE_max = 1.462%) in their solution-processable doped OLEDs. This work demonstrates a straightforward and efficient approach for the development of highly efficient red TADF emitters.