Doubly Boron‐Doped TADF Emitters Decorated with ortho‐Donor Groups for Highly Efficient Green to Red OLEDs

Abstract

Doubly boron‐doped thermally activated delayed fluorescence (TADF) emitters based on a 9,10‐diboraanthracene (DBA) acceptor decorated with ortho‐donor groups (Cz2oDBA, 2; BuCz2oDBA, 3; DMAC2oDBA, 4) are prepared to realize high‐efficiency green‐to‐red organic light‐emitting diodes (OLEDs). X‐ray diffraction analyses of 2 and 4 reveal the symmetrical and highly twisted ortho‐donor–acceptor–donor (D‐A‐D) structure of the emitters. The twisted conformation leads to a very small energy splitting (ΔEST <0.08 eV) between the excited singlet and triplet states that gives rise to strong TADF, as supported by theoretical studies. Depending on the strength of the donor moieties, the emission color is fine‐tuned in the visible region from green (2) to yellow (3) to red (4). Carbazole‐containing 2 and 3 exhibit high photoluminescence quantum yields (PLQYs) approaching 100 %, whereas DMAC‐substituted 4 is moderately emissive (PLQY=44 %) in a doped host film. Highly efficient green‐to‐red TADF‐OLEDs are realized with the proposed ortho‐D‐A‐D compounds as emitters. The green and yellow OLEDs incorporating Cz2oDBA (2) and BuCz2oDBA (3) emitters exhibit high external quantum efficiencies (EQEs) of 26.6 % and 21.6 %, respectively. In particular, the green device shows an excellent power efficiency above 100 lm W−1. A red OLED fabricated with a DMAC2oDBA (4) emitter exhibits a maximum EQE of 10.1 % with an electroluminescence peak at 615 nm.

Molecular Design Strategy for Orange Red Thermally Activated Delayed Fluorescence Emitters in Organic Light‐Emitting Diodes (OLEDs)

“…In 2020, Lee et al investigated the doubly boron-doped thermally activated delayed fluorescence (TADF) emitters based on a 9,10-diboraanthracene (DBA) acceptor decorated with ortho substituted acridine donor based [39] DMAC2oDBA. Due to the twisted molecular configuration, a good TADF performance Chemistry-A European Journal was obtained with the support of a small ~EST .…”

Versatile boron‐based thermally activated delayed fluorescence materials for organic light‐emitting diodes

“…In a related work, Lee and coworkers designed another DBA derivative 151 by introducing ortho ‐donor groups to the acceptor, which showed strong green emission with the PLQYs nearly 100% in both solution and film state. [ 104 ] Although emission spectra of the doped films exhibited a small redshift with the increase of the doping concentration of compound 151 , the PLQY still as high as 100%. A green OLED device based on the emitter 151 (λ EL = 544 nm) achieved a maximum EQE of up to 26.6% and a desirable power efficiency over 100 lm W –1 .…”

Acceptor–Donor–Acceptor‐Type Orange–Red Thermally Activated Delayed Fluorescence Materials Realizing External Quantum Efficiency Over 30% with Low Efficiency Roll‐Off

“…[ 14 ] Additionally, boron compounds with a linear quadrupolar D–A–D or A–D–A molecular configuration would be useful to shift the emission to the red region as well as to increase the horizontal dipole orientation. [ 15 ] Recently, Cheng and co‐workers reported D–A–D configured diboron acceptor‐based orange–red TADF emitters with maximum EQE of 30.0% with maximum EL at 567 nm [ 4 ] and this is the highest efficiency among orange to red TADF OLEDs. Thus, considering these things in mind, we designed new linear A–D–A boron‐based TADF materials, 5,10‐bis(2,12‐di‐ tert ‐butyl‐5,9‐dioxa‐13 b ‐boranaphtho[3,2,1‐ de ]anthracen‐7‐yl)‐5,10‐dihydrophenazine (PzTDBA) and 5,10‐di(5,9‐dioxa‐13 b ‐boranaphtho[3,2,1‐ de ]anthracen‐7‐yl)‐5,10‐dihydrophenazine (PzDBA), for orange–red OLEDs.…”

“…It is interesting to note that the k risc is on the order of 10 6 s −1 reflecting the simulation results, and this k risc value is high compared to other red TADF materials. [4,8,5,15] In order to find the reason for the fast k risc value, the spin-orbit coupling matrix element (SOCME) <S 1 |Ĥ SOC | T 1 > of these two materials were calculated by following the literature. [19] The calculated value of < 1 CT|Ĥ SOC | 3 CT> is 0.002 cm −1 for PzDBA and 0.002 cm −1 for PzTDBA.…”