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

Abstract

The meta junction is proposed to realize efficient thermally activated delayed fluorescence (TADF) in donor–acceptor (D‐A) conjugated polymers. Based on triphenylamine as D and dicyanobenzene as A, as a proof of concept, a series of D‐A conjugated polymers has been developed by changing their connection sites. When the junction between D and A is tuned from para to meta, the singlet–triplet energy splitting (ΔEST) is found to be significantly decreased from 0.44 to 0.10 eV because of the increasing hole–electron separation. Unlike the para‐linked analogue with no TADF, consequently, the meta‐linked polymer shows a strong delayed fluorescence. Its corresponding solution‐processed organic light‐emitting diodes (OLEDs) achieve a promising external quantum efficiency (EQE) of 15.4 % (51.9 cd A−1, 50.9 lm W−1) and CIE coordinates of (0.34, 0.57). The results highlight the bright future of D‐A conjugated polymers used for TADF OLEDs.

Sterically‐Locked Donor–Acceptor Conjugated Polymers Showing Efficient Thermally Activated Delayed Fluorescence

“…Same with our previous work, [13] only prompt fluorescence appears in poly(TPAp–DCBp) because of the large Δ E ST (Figure 4 a). With the decreasing Δ E ST induced by the methyl hindrance, both prompt and delayed fluorescence can be recorded for poly(DMTPA–DCB) and poly(TMTPA–DCB).…”

“…Attributable to these advantages, high‐performance organic solar cells (OSCs) [4–6] and organic thin film transistors (OTFTs) [7, 8] have been successfully realized on the basis of D–A conjugated polymers. However, their potential in organic light‐emitting diodes (OLEDs) is seldom investigated 9 , especially in thermally activated delayed fluorescence (TADF) OLEDs [10–13] …”

Sterically‐Locked Donor–Acceptor Conjugated Polymers Showing Efficient Thermally Activated Delayed Fluorescence

“…demonstrated the admixture of n‐orbitals early in 2016, and reported benzophenone‐based TADF polymers with a small Δ E ST below 0.2 eV and a maximum external quantum efficiency (EQE) of 9.3 % [10] (Figure 1). Recently, our group has developed a meta junction to achieve efficient TADF in D–A conjugated polymers [13] . As the junction between donor and acceptor is varied from para to meta, the Δ E ST is determined to be reduced from 0.44 to 0.10 eV.…”

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

“…The short distance between donor and acceptor unit together with localized distribution of LUMOs on the electron-deficient benzene ring may induce considerable electronic coupling and HOMO-LUMO spatial overlap, which is essential for efficient TADF molecules via TSCT process. [13] These results indicate that the chiral spiro-axis skeleton may not only introduce CPL property into TADF molecules but also promote intramolecular TSCT process. Furthermore, good thermal stability was verified by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC); decomposition temperature was determined to be 285 8C (Supporting Information, Figure S10).…”

“…Therefore, the chiral spiro-axis structure should be more suitable for developing CP-TADF materials. 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 Liaos group.…”