Chiral multiple-resonance thermally activated delayed fluorescence materials based on chiral spiro-axis skeleton for efficient circularly polarized electroluminescence

Chiral luminescence materials have potential applications in the field of three-dimensional displays due to their circularly polarized luminescence (CPL) characteristics. However, the further development of circularly polarized organic light-emitting diodes (CP-OLEDs) needs to meet the requirements of high efficiency, high color purity, low cost, and high dissymmetry factor (g_PL or g_EL), chiral multiple resonance thermally activated delayed fluorescence (MR-TADF) materials are considered as candidates in these aspects. Herein, based on a pair of chiral spirofluorene precursors, two pairs of high-performance chiral MR-TADF emitters ((R/S)-p-Spiro-DtBuCzB and (R/S)-m-Spiro-DtBuCzB) are developed, which exhibit strong emissions peaking at 491 and 502 nm in toluene with full-width at half-maximum values of 25 and 33 nm, respectively. In addition, small singlet–triplet energy gaps of 0.15 and 0.10 eV with high absolute photoluminescence efficiencies of 95.0% and 96.7% are observed for p-Spiro-DtBuCzB and m-Spiro-DtBuCzB molecules, respectively. OLEDs based on p-Spiro-DtBuCzB and m-Spiro-DtBuCzB display high maximum external quantum efficiencies of 29.6% and 33.8%, respectively. Most importantly, CP-OLEDs present symmetric circularly polarized electroluminescence spectra with ∣g_EL∣ factors of 3.36×10⁻⁴ and 7.66×10⁻⁴ for devices based on (R/S)-p-Spiro-DtBuCzB and (R/S)-m-Spiro-DtBuCzB enantiomers, respectively.