Multi‐Layer π‐Stacked Molecules as Efficient Thermally Activated Delayed Fluorescence Emitters

Abstract

Multi-layer p-stacked emitters based on spatially confined donor/acceptor/donor (D/A/D) patterns have been developed to achieve high-efficiency thermally activated delayed fluorescence (TADF). In this case, dual donor moieties and a single acceptor moiety are introduced to form two threedimensional (3D) emitters, DM-BD1 and DM-BD2, which rely on spatial charge transfer (CT). Owing to the enforced face-to-face D/A/D pattern, effective CT interactions are realized, which lead to high photoluminescence quantum yields (PLQYs) of 94.2 % and 92.8 % for the two molecules, respectively. The resulting emitters exhibit small singlet-triplet energy splitting (DE ST) and fast reverse intersystem crossing (RISC) processes. Maximum external quantum efficiencies (EQEs) of 28.0 % and 26.6 % were realized for devices based on DM-BD1 and DM-BD2, respectively, which are higher than those of their D/A-type analogues.

Chiral Spiro‐Axis Induced Blue Thermally Activated Delayed Fluorescence Material for Efficient Circularly Polarized OLEDs with Low Efficiency Roll‐Off

“…However, spiro‐type TADF molecules containing through space charge transfer (TSCT) process [13] normally suffer from obvious device efficiency roll‐off. Quite recently, great progresses have been made by Jiang and Liao's group [10b, 13a,d–f] . Via a parallel surface strategy, TSCT process is successfully enhanced and some devices exhibit EQE max over 20 % with low efficiency roll‐off [10b, 13a,e,f,i] .…”

“…Quite recently, great progresses have been made by Jiang and Liao's group [10b, 13a,d–f] . Via a parallel surface strategy, TSCT process is successfully enhanced and some devices exhibit EQE max over 20 % with low efficiency roll‐off [10b, 13a,e,f,i] . However, this type of TADF molecules usually display greenish emission, efficient TSCT based TADF molecule with blue emission still remains scarce.…”

The Impact of C2 Insertion into a Carbazole Donor on the Physicochemical Properties of Dibenzo[a,j]phenazine‐Cored Donor–Acceptor–Donor Triads

“…In stark contrast to Cz, iminodibenzyl (IDB) and iminostilbene (ISB), which are C 2 -inserted homologues of Cz, [4] have been much less explored as electron donors in D-A twisted type organic functional materials. [5][6][7] In 2018, Dias and Grazulevicius reported that the attachment of ISB and IDB donors to quinoxaline acceptor unit allows unique mechanochromic luminescence properties and dual TADF and roomtemperature phosphorescence (RTP). [5] Independently, Bryce and Monkman investigated the influence of introducing ISB donor onto the 9,9-dimethylthioxanthene-S,S-dioxide (TXO2) acceptor unit on the structure and TADF properties of the D-A-D compounds in comparison with other analogous donors, thus suggesting the importance of conformations in blue TADF.…”

“…[6] They showcased that IDB donor lies between diphenylamine and dihydroacridine donors in terms of electron-donating ability and conformational flexibility. And recently, Kaji and coworkers disclosed the utilization of IDB in through-space charge-transfer (TSCT) TADF [7] material which is featured with very efficient reverse intersystem crossing (rISC). [8] Nevertheless, any other systematic studies of the influence of the C 2 insertion into the Cz unit on the physicochemical properties of D-A type compounds have not been clarified.…”

Thermally Activated Delayed Fluorescence beyond Through‐Bond Charge Transfer for High‐Performance OLEDs

“…To further enhance the intra-TSCT effect, the multiple π-stacked TADF emitters DM-BD1 and DM-BD2 (Figure 17e), featuring the donor-acceptor-donor 3D scaffold linked by the two fluorenyl units, were developed. [109] The calculated ΔE ST s Adachi's group designed and synthesized the spirobased TADF emitter QAFCN where the rigid donor 5,9-dihydroquinolino[3,2,1-de]acridine displayed the deformed configuration (Figure 18). [110] It was supposed that the greatly shortened spatial separation between the donor and the acceptor would further promote the intra-TSCT.…”