Constructing High‐Efficiency Orange‐Red Thermally Activated Delayed Fluorescence Polymers by Excited State Energy Levels Regulation via Backbone Engineering

Abstract

Thermally activated delayed fluorescence (TADF) materials have attracted extensive attention because of their 100% theoretical exciton utilization. Solution‐processable orange‐red TADF polymers are one of indispensable participants. Herein, a series of orange‐red TADF polymers with dibenzothiophene (DBT) and carbazole (Cz) units as joint backbones are synthesized. Their performance can be successfully optimized by regulating the connection positions of DBT units through backbone engineering. It is found that the pNAI37 series with DBT units embedded in the polymeric backbones at the 3, 7 sites display a better performance than those connected at the 2, 8 sites. The optimal polymer, pNAI3705, exhibits a better excited state nature, leading to the photoluminescence quantum yield of 60%. Consequently, pNAI3705 based organic light‐emitting diodes reach a maximum external quantum efficiency of 20.16%, and maintain 10.61% at 500 cd m−2, which is in first tier among orange‐red polymers. These results unambiguously suggest the potential application of the combined DBT and Cz backbones in TADF polymers. This design strategy may provide a versatile approach for optimizing the properties of TADF polymers through backbone engineering.

Recent advances in regulating the excited states of conjugated thermally activated delayed fluorescence polymers for high-efficiency OLEDs

“…Then, pNAI37 series and pNAI28 series orange-red TADF polymers are synthesized with joint backbones of dibenzothiophene (DBT) and carbazole (Cz). 38 By adjusting the connecting position of the DBT unit, the polymeric performance is successfully optimized. Meanwhile, the 1 CT and 3 CT levels of pNAI37 series are both 17 meV higher than those of the pNAI28 series, however, the pNAI37 series presents a smaller energy gap between the 1 CT and 3 LE levels [Δ E ( 1 CT– 3 LE)] than the pNAI28 series.…”

Intramolecular Sensitization Assisting High-Efficiency TADF Conjugated Polymers with Accelerating Exciton Spin Flip for Solution-Processed Electroluminescent Devices

“…From previous works, it also can be concluded that the donor moieties of TADF molecules are greatly affected by the adjacent host units in the conjugated backbone once the TADF molecules are integrated into it. , The conjugation extension of the polymer backbone will increase the overlap of molecular orbitals during the electron transition, resulting in a larger energy gap between singlet and triplet states (Δ E ST ), which will inhibit RISC process and weaken the optoelectrical properties of polymeric emitters. ,, In this context, we also construct conjugated TADF polymers by embedding spirofluorene units into a conjugated backbone and connecting the TADF side chains to the backbone by sp3 carbon atoms . Therefore, the isolation between the TADF unit and the polymer backbone can be effectively ensured, and the TADF characteristics of the monomer can be effectively inherited into polymers.…”

“…As a critical building block for large-area and low-cost flexible display, polymer-based light-emitting diodes (PLEDs) have generated intense attention. − In contrast with traditional PLEDs adopting low-efficiency fluorescent polymers or noble-metal-based phosphorescent polymers as emitters, purely organic thermally activated delayed fluorescence (TADF) polymers allow for 100% internal quantum efficiency by integrally harnessing singlet and triplet excitons, in which the triplet excitons can upconvert to an emissive state via a reverse intersystem crossing (RISC) process. − Especially for TADF conjugated polymers, intrinsic delocalized backbones provide ideal electrical channels for rapidly delivering carriers and subsequently sufficiently generating excitons. Therefore, a high-efficiency TADF conjugated polymer-based electroluminescent (EL) device can be achieved by accurately modulating the composition of conjugated skeletons and TADF segments to make the most possible use of carriers and excitons. − …”

“…Hua et al presented a series of orange-red TADF polymers with dibenzothiophene (DBT) and carbazole units as joint backbones, and the excited-state energy levels and properties of TADF polymers can effectively be regulated by regulating the connection positions of DBT units through backbone engineering. Thus, a more efficient dual RISC channel can be established to improve the performance …”

Chiral Polyacetylene with Thermally Activated Delayed Fluorescence Feature for High-Performance Circularly Polarized Light Detection

“…Thermally activated delayed fluorescent (TADF) materials are a prototype class of organic semiconductors that can harvest both singlet (S 1 ) and T 1 excitons via the reverse intersystem crossing (RISC) process, yielding a theoretical internal quantum efficiency (IQE) of 100%. − Benefiting from the effective excitons harvesting, TADF materials have made significant advancements in organic OLEDs, with multiple record-breaking works published in the fields of maximum external quantum efficiency (EQE max ) and high color purity. − Furthermore, the TADF polymers with a small energy gap between S 1 and T 1 (Δ E ST , generally less than 0.2 eV) can boost up-conversion from T 1 to S 1 , which is favorable for their efficient recycled ISC and RISC processes. Exciton quenching, especially for triplet–triplet annihilation caused by high concentration aggregation, can thus be suppressed due to the exciton recycling process.…”