Triarylboron‐Based Fluorescent Organic Light‐Emitting Diodes with External Quantum Efficiencies Exceeding 20 %

Abstract

Triarylboron compounds have attracted much attention, and found wide use as functional materials because of their electron-accepting properties arising from the vacant p orbitals on the boron atoms. In this study, we design and synthesize new donor-acceptor triarylboron emitters that show thermally activated delayed fluorescence. These emitters display sky-blue to green emission and high photoluminescence quantum yields of 87-100 % in host matrices. Organic light-emitting diodes using these emitting molecules as dopants exhibit high external quantum efficiencies of 14.0-22.8 %, which originate from efficient up-conversion from triplet to singlet states and subsequent efficient radiative decay from singlet to ground states.

Donor–σ–Acceptor Motifs: Thermally Activated Delayed Fluorescence Emitters with Dual Upconversion

“…Recently,t he application of metal-free thermally activated delayed fluorescence (TADF) emitters has led to the development of TADF OLEDs,w hich are among the most promising classes of practical next-generation OLEDs,s ince high-performance EL characteristics can be obtained through the molecular design of conventional aromatic compounds, which is in principle unlimited. [6] TheT ADF process is central to the formation of ac harge-transfer (CT) excited state from donor-acceptor (D-A) molecules,i nw hich the highest occupied molecular orbital (HOMO) is located on the donor moiety,a nd the lowest unoccupied molecular orbital (LUMO) is offered by the acceptor moiety.F or conventional D-A-type TADF emitters,t he overlap between HOMO and LUMO must be minimized to decrease the DE ST value,w hich is crucial for efficient thermal upconversion through RISC. [5] Recently,s ubstantial progress has been made with TADF OLEDs.Anexternal EL quantum efficiencyofover 30 %has been reached, which is comparable with that of the best PHOLEDs.…”

Electronic and Photophysical Properties of 9,10‐Anthrylene‐Bridged B‐π‐N Donor‐Acceptor Molecules with Solid‐State Emission in the Yellow to Red Region

“…On the other hand, the lone pair electron occupying p‐orbital of nitrogen, p(N), delivers a strong electron‐donating capability of triarylamine, and the triarylamine‐based materials have been widely exploited as hole‐transport materials in optoelectronic devices . Within this context, a variety of D‐π‐A molecular systems ranging from the simple B‐π‐N structured molecules to the extended π‐conjugated molecular systems where the B‐π‐N units are multiply embedded, have been prepared and, furthermore, they have demonstrated intriguing intramolecular charge transfer (ICT) behaviors upon photoexcitation, although their origin dates back to the early 1970s, when Williams and co‐workers at Kodak conducted the pioneering work …”

“…Generally, to overcome the obstacle of ACQ, there exist several molecular design strategies, and one of them is to prepare sterically overcrowded molecules by vicinal substitution of aryl groups on π‐bridging units and/or introduction of bulky extended polycyclic aromatic core, so as to isolate each fluorophore in the solid state. With this strategy in mind, we have decided to embark upon reinvestigation of electronic and photophysical properties on 9,10‐anthrylene‐bridged simple B‐π‐N type molecules, 1 and 2 (Scheme ), which are closely related to the hitherto known compounds, though diphenylamine groups in 1 and 2 are terminated by tert ‐butyl groups to improve the stability of their oxidized states, thereby also leading to suppression of intermolecular interactions in the solid state.…”

“…[3] On the other hand, the lone pair electron occupying p-orbital of nitrogen, p (N), delivers a strong electron-donating capability of triarylamine, and the triarylamine-based materials have been widely exploited as hole-transport materials in optoelectronic devices. [4] Within this context, a variety of D-π-A molecular systems ranging from the simple B-π-N structured molecules to the extended π-conjugated molecular systems where the B-π-N units are multiply embedded, have been prepared and, furthermore, they have demonstrated intriguing intramolecular charge transfer (ICT) behaviors upon photoexcitation, [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] although their origin dates back to the early 1970s, when Williams and co-workers at Kodak conducted the pioneering work. [24] Although solution-state emissive properties have been so far mainly examined for these B-π-N type compounds, solidstate emissive organic fluorophores have also attracted intensive research interest due to their widespread applications in the field of organic electronics.…”

Design and Synthesis of New Circularly Polarized Thermally Activated Delayed Fluorescence Emitters

“…This property has recently motivated numerous research works because of the theoretical possibility to develop organic light emitting diodes (OLEDs) with maximum efficiency. 3 The conception of CPL-SOMs is also a great challenge for organic chemists. Currently, only a small number of CPL-SOMs display high performance both in terms of quantum yield ( ϕ F ) and luminescence dissymmetry factor ( g lum ).…”