Asymmetric Spirobiacridine‐based Delayed Fluorescence Emitters for High‐performance Organic Light‐Emitting Devices

Abstract

Recently, researchers have focused on thermally activated delayed fluorescence (TADF) for efficient future lighting and displays. Among TADF emitters, a combination of triazine and acridine is a promising candidate for realizing high-efficiency organic light-emitting devices (OLEDs). However, simultaneous development of perfect horizontal orientation (Θ = 100 %) and an external quantum efficiency (EQE) of over 40 % is still challenging. Here, to obtain insights for further improvements of a triazine/acridine combination, various asymmetric spirobiacridine (SBA)-based TADF emitters with a unity photoluminescence quantum yield and high Θ ratio of over 80 % were developed. Furthermore, the substitution effects of the triazine acceptor unit on the photophysical properties were studied, including molecular orientations and OLED performance. The corresponding OLED exhibited sky-blue emission with a high EQE of over 30 %.

1,3,5‐Triazine‐Functionalized Thermally Activated Delayed Fluorescence Emitters for Organic Light‐Emitting Diodes

“…A similar design using SBA as the donor and triazine as the acceptor has also been explored by Kido et al [ 37 ] to enable the horizontal orientation of the TDM of emitters in OLEDs. Three molecules, tBuTZ‐SBA‐Ph , TZ‐SBA‐Ph, and tBuPhTZ‐SBA‐Ph, were prepared with the difference in structure associated with the choice of distal groups on the triazine acceptor unit.…”

“…d) The direction of the calculated S 0 ÀS 1 transition dipole moment. Reproduced with permission [37]. Copyright 2021, Wiley-VCH.…”

Introducing Spiro‐locks into the Nitrogen/Carbonyl System towards Efficient Narrowband Deep‐blue Multi‐resonance TADF Emitters

“…These results agree with the experimental HOMO energy levels ensured by DPV curves and are also similar to other reported spiro compounds. [28] Excited state analyses were also conducted to analyze the emission mechanism. Spin component scaling secondorder approximate Coupled-Cluster (SCS-CC2) calculations at the cc-pVDZ level were used to reveal the excited state energy levels.…”

Construction of Annulated Spiro[4.4]-nonane-diones via the Tandem [4 + 2]-Cycloaddition/Aromatization Reaction

“…Spirocycle 3 offers a convenient platform for the synthesis of unsymmetrical π-conjugated spirocycles with electron-donating and electron-withdrawing subsystems, which can possess unique optoelectronic properties such as TADF or singlet fission. ,, It makes the problem of addition selectivity (the ratio of mono- to di-[4 + 2]-addition product) a top priority. Thus, the product of di-cycloaddition/aromatization 20b can be obtained using the stoichiometric amounts of IBF and spirocycle 3 .…”

“…Spirocyclic compounds (e.g., 2,2′-spirobi­[indene] derivatives) have attracted much attention among synthetic chemists over the decades. − This structurally rigid motif can be found in both various natural products with a diversity of biological activities and artificial molecules with unique optoelectronic properties. ,− Incorporation of the spirocyclic moieties into organic light-emitting molecules or conjugated polymers improves their performance in light-emitting diodes (OLEDs) since the “three-dimensional” structure of a spiro center increases molecular rigidity, leading to a high photoluminescence quantum yield and high horizontal dipole orientation. Moreover, spiro junction suppresses excimer formation and provides color purity improvement due to the narrowing of the material’s emission bands, which allows the construction of metal-free organic thermally activated delayed fluorescence (TADF) materials. ,,, …”