Simple Double Hetero[5]helicenes Realize Highly Efficient and Narrowband Circularly Polarized Organic Light-Emitting Diodes

Abstract

Helicene-based emitters with unique inherent circularly polarized luminescence (CPL) are promising yet remain a formidable challenge for highly efficient circularly polarized organic light emitting diodes (CP-OLEDs), ascribed to their tough synthesis, low emission efficiency, and easy racemization in thermal deposition process. Herein, a pair of helicene-based enantiomers, namely (P)-helicene-BN and (M)-helicene-BN, were developed, which merge helical chirality and the B/N/S inserted polycyclic aromatic framework to concurrently feature CPL and narrow thermally activated delayed fluorescence (TADF) characteristics. Benefiting from the excellent thermal/photophysical/chiroptical properties, the narrowband green CP-OLEDs based on the enantiomers achieved maximum external quantum efficiencies (EQE max ) of up to 31.5%, and dissymmetry factor (|g EL |) of 2.2 × 10 -3 . This work reveals the great potential of helicene-based emitters in CP-OLEDs.

Advances in circularly polarized electroluminescence based on chiral TADF-active materials

“…11), characterized by a B/N/S embedded polycyclic fused aromatic skeleton. 54 P / M - helicene-BN displayed obvious MR-TADF and CPL properties. The CP-OLEDs emitted green EL ( λ EL = 520 nm) with a narrow FWHM of 49 nm, extremely high EQE max of up to 31.5%, as well as CPEL signals with | g EL | of 2.2 × 10 −3 .…”

Narrowband Emissive Thermally Activated Delayed Fluorescence Materials

“…Apart from RISC acceleration via the heavy‐atom effect of S atoms, intriguing chiroptical properties based on the helical nature of S‐bridged MR frameworks were recently found. [ 96,102 ] In 2022, Chou and co‐workers reported two CPL‐active MR‐TADF emitters, BN4 and BN5 [ 96 ] (Figure 7), which exhibited narrowband green TADF emissions (λ PL = 500/497 nm, FWHM PL = 43/44 nm, and Φ PL = 88%/87%, respectively, in toluene) with relatively high k RISC values of ≈10 5 s −1 . Because of the sufficient racemization barriers induced by the asymmetrical peripheral lock, the separation of enantiomers into (−)( P , P′ , P″ )‐ and (+)( M , M′ , M″ )‐atropisomers was possible.…”

“…Most recently, MR-TADF materials containing S atom(s), a third-period element, have received particular attention. [83,[94][95][96][97][98][99][100][101][102][103] This is primarily because the incorporation of heavier S atom(s) facilitates spinflip RISC via the heavy-atom effect in several D-A type TADF materials. [24,[104][105][106] The first S-doped MR-TADF materials, BSBS-N1 [94] and 2PTZBN [95] (Figure 7), were reported by Yasuda's group and Yang's group, respectively, around the same time in 2021.…”

Boron‐Based Narrowband Multiresonance Delayed Fluorescent Emitters for Organic Light‐Emitting Diodes

“…However, due to the cotton Yang et al reported a pair of helicene-based enantiomers, namely, (P)-helicene-BN and (M)-helicene-BN. [123] The design is based on merging the helical chirality with B/N/S-inserted PAH skeleton. The designed emitter exhibited narrowband green emission with an FWHM of 46 nm.…”