Efficient Circularly Polarized Electroluminescence from Chiral Thermally Activated Delayed Fluorescence Emitters Featuring Symmetrical and Rigid Coplanar Acceptors

Abstract

Circularly polarized organic light‐emitting diodes (CP‐OLEDs) that enable circularly polarized luminescence (CPL) are promising for 3D display and photonic applications. However, the device efficiency and CPL character of CP‐OLEDs still lag behind the practical requirements. Here, two pairs of axially chiral emitting enantiomers, flexible (R/S)‐ODQPXZ and rigid (R/S)‐ODPPXZ, are reported by fusing (R/S)‐octahydro‐binaphthol chiral source, diphenyl quinoxaline (DQ)/dibenzo[a,c]phenazine (DP) acceptors and phenoxazine (PXZ) donors. The symmetrical chiral‐acceptor‐donor configuration endows them thermally activated delayed fluorescence (TADF) properties with small singlet–triplet energy gaps of 0.16 and 0.07 eV, high photoluminescence quantum yields of 92% and 89% in doped films, and obvious mirror‐image CPL characteristics, respectively. The CP‐OLEDs based on these TADF enantiomers not only show a maximum external quantum efficiency of 28.3% with yellow emission for (R/S)‐ODQPXZ and 20.3% with orange‐red emission for (R/S)‐ODPPXZ, but also display the CPL with dissymmetry factors (gEL) of 6.0 × 10−4 and 2.4 × 10−3, respectively. The high efficiency and obvious CPL of (R)‐ODPPXZ arise from a synergetic interplay of the TADF skeleton and the rigid coplanar acceptor for efficient chiral induction and suppressed intramolecular rotational quenching.

Frontiers in circularly polarized luminescence: molecular design, self-assembly, nanomaterials, and applications

“…In . To improve the device efficiency, researchers also applied double emissive layers in CP-OLEDs for chiral Pt(II) complexes [307] and TADF materials [308][309][310][311][312]. For example, in 2020 Zheng and co-workers [307] prepared a pair of deepred platinahelicene enantiomers (P/M)-80 peaking at 653 nm, which showed a |g lum | of 6 × 10 To present, most CP-OLEDs show lower g EL than g lum factors, except for the chirality transfer from the guest to host.…”

Planar Chiral [2.2]Paracyclophane-Based Thermally Activated Delayed Fluorescent Materials for Circularly Polarized Electroluminescence

“…Among them, circular polarized organic light emitting diodes (CP-OLEDs) have become an attractive direction because of their high performance. Therefore, many CP-OLED materials with different designs have been developed since the first report in 1997, including chiral polymers, − chiral emissive small molecules, − and chiral complexes. − However, they suffered from insufficient quantum efficiency or low dissymmetry factor ( g lum or g EL ). Therefore, it is highly desirable to develop CP-OLEDs materials with both intense dissymmetry factors ( g EL ) and high external quantum efficiencies (EQE). , …”

Controllable Circularly Polarized Electroluminescence Performance Improved by the Dihedral Angle of Chiral-Bridged Binaphthyl-Type Dopant Inducers

“…Circularly polarized organic light-emitting diodes (CP-OLEDs) have already focused on the potential application prospect in areas such as optical-information storage and processing, field-effect transistor detection devices for circularly polarized light (CPL), bio-responsive imaging systems, and 3D displays. , Up to now, versatile organic circularly polarized electroluminescence (CP-EL) emitters, including organic small dyes, − heavy metal-containing complexes, − and conjugated fluorescence polymers, − have been smartly designed by introducing the chiral units into achiral chromophore skeleton or blending chiral inducers with achiral conjugated fluorescent polymers and have been successfully applied for CP-OLEDs. However, most of the organic CP-EL small emitters suffered from the dissatisfactory CP-EL performances with inferior efficiencies or low CP-EL dissymmetry factor ( g EL ), which greatly limits their practical applications. − Recently, using achiral fluorescence polymers as CP-EL emitters have received much attention due to their low cost and facile device fabrication process. − Therefore, the development of CP-OLEDs based on achiral fluorescence polymers with intense g EL values is of great significance via the chirality induction mechanism.…”