Tri‐Spiral Donor for High Efficiency and Versatile Blue Thermally Activated Delayed Fluorescence Materials

Abstract

Blue thermally activated delayed fluorescence (TADF) emitters that can simultaneously achieve high efficiency in doped and nondoped organic light‐emitting diodes (OLEDs) are rarely reported. Reported here is a strategy using a tri‐spiral donor for such versatile blue TADF emitters. Impressively, by simply extending the nonconjugated fragment and molecular length, aggregation‐caused emission quenching (ACQ) can be greatly alleviated to achieve as high as a 90 % horizontal orientation dipole ratio and external quantum efficiencies (EQEs) of up to 33.3 % in doped and 20.0 % in nondoped sky‐blue TADF‐OLEDs. More fascinatingly, a high‐efficiency purely organic white OLED with an outstanding EQE of up to 22.8 % was also achieved by employing TspiroS‐TRZ as a blue emitter and an assistant host. This compound is the first blue TADF emitter that can simultaneously achieve high electroluminescence (EL) efficiency in doped, nondoped sky‐blue, and white TADF‐OLEDs.

Meta Junction Promoting Efficient Thermally Activated Delayed Fluorescence in Donor‐Acceptor Conjugated Polymers

“…At first, 4-octylaniline was reacted with 1bromo-4-iodobenzene and 1-bromo-3-iodobenzene via aB uchwald-Hartwig C-N coupling [37] to get 4-bromo-N-(4bromophenyl)-N-(4-octylphenyl)aniline (1)a nd 3-bromo-N-(3-bromophenyl)-N-(4-octylphenyl)aniline (2), which were then converted to their corresponding borate monomers M1 and M2 by esterification, respectively.W ith the bromide monomers 2,5-dibromoterephthalonitrilea nd 2,6-dibromoterephthalonitrile in hand, at ypical Suzuki polymerization [38,39] was then performed to afford four polymers with different D-A junctions,n amely poly(TPAp-DCBp), poly(-TPAp-DCBm), poly(TPAm-DCBp) and poly(TPAm-DCBm). Them olecular structures of these polymers were characterized by gel permeation chromatography (GPC), 1 H and 13 CNMR, and elementary analysis.T he number-average weight (M n )r anges from 4.1 kDa to 13.1 kDa with polydispersity index (PDI) from 1.29 to 1.92 (Table 1). Noticeably, the meta-involved polymers poly(TPAp-DCBm), poly(-TPAm-DCBp) and poly(TPAm-DCBm) seem to have asmaller M n than that of poly(TPAp-DCBp).…”

“…[8,9] Also,t he electronic coupling between the local triplet and the charge transfer states together with the effect of dynamic rocking of the D-A units about the orthogonal geometry plays ac rucial role on the achievement of efficient TADF. [10] On the basis of these criteria, ag reat number of TADF small molecules [11][12][13][14][15][16][17] have been successfully reported to give various emission colors in the whole visible region as well as comparable electroluminescent device efficiencies to phosphors. [18,19] Starting from Da nd A, however,i tr emains ab ig challenge to design TADF polymers that are suitable for low-cost and easily scalable wet methods ( Figure 1).…”

Structural Design of Blue‐to‐Red Thermally‐Activated Delayed Fluorescence Molecules by Adjusting the Strength between Donor and Acceptor

“…Su et al synthesized two high-efficient blue TADF materials (TspiroS-TRZ and TspiroS-TRZ) with two long bar-shaped donor units and an acceptor moiety of TRZ ( Figure 3). [40] The devices based on TspiroS-TRZ and TspiroF-TRZ exhibit sky-blue emissions with the peaks at 481 and 493 nm. Compare to TspiroF-TRZ, TspiroS-TRZ has a blue-shifted EL spectra, which can be attributed to the weaker electron-donating ability of spiro[anthracene-9,9'-thioxanthene] than that of spiro [anthracene-9,9'-fluorene].…”

Asymmetric-donor (D2D2′)–acceptor (A) conjugates for simultaneously accessing intrinsic blue-RTP and blue-TADF

“…Recently, organic donor-acceptor (D-A) based emitters with a thermally activated delayed fluorescence (TADF) [6][7][8][9][10][11] feature that occurs via reverse intersystem crossing (rISC) from either the higher lying triplet state (T n , n 4 1) [6][7][8] or the lowest triplet (T 1 ) state to the lowest singlet (S 1 ) state, [9][10][11] have showed exciting capabilities for energy-efficient light emission by harvesting of both singlet and triplet states. To harness the triplet exciton via TADF, numerous research studies have been undertaken, which have established that apart from the low S 1 -T 1 gap between the singlet and triplet states, the nonadiabatic effect between the low-lying excited states along with mixing of the intermediate excited states plays a crucial role in the process of ISC and rISC.…”