Axial enantiomers with donor-regulated TADF feature for multicolor circularly polarized electroluminescence

This study optimized the TADF feature of axial chiral enantiomers through precise donor engineering, and multicolor CP-TADF was achieved in the axial chiral framework. Three pairs of axial enantiomers with donor-regulated TADF feature, namely (R/S)-TPCBD, (R/S)-DPCBD, and (R/S)-DPACBD, were synthesized by introducing carbazole donors with different substituents onto biphenyl cyanide acceptors. As the electron-donating ability of donors increases, the emission of these axial enantiomers ranges from 455,476 to 552 nm, their singlet-triplet energy gaps (ΔE_ST) gradually decrease from 0.30,0.22 to 0.02 eV, accompanied by an increasement in the transition rate (k_RISC) of RISC process, and the k_RISC of DPACBD could reach up to 7.16 × 10⁵ s⁻¹. These axial enantiomers also exhibit mirror-image CD and circularly polarized luminescence (CPL) properties. Moreover, OLEDs based on TPCBD, DPCBD, and DPACBD as emitter were then fabricated, which displayed blue, green, and orange electroluminescence with EQE_max of 13.0%, 16.4%, and 25.0%, respectively. The results also exhibited a phenomenon of device efficiency increasing with the enhancement of donor abilities. Notably, the CP-OLEDs using (R/S)-TPCBD, (R/S)-DPCBD and (R/S)-DPACBD as emitters displayed intense CPEL signals with g_EL values of 3.4 × 10⁻³/−4.1 × 10⁻³, 3.2 × 10⁻³/−3.1 × 10⁻³ and 2.3 × 10⁻³/−2.1 × 10⁻³, respectively. By convenient molecular engineering of donor regulation in the same molecular skeleton, CP-TADF materials with multicolor CPEL and improved device performance could be conveniently achieved.