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

Abstract

Donor–acceptor (D–A) conjugated polymers often possess a significant frontier molecular orbital overlap because of the conjugation elongation, leading to no thermally activated delayed fluorescence (TADF) caused by a large singlet‐triplet energy splitting (▵EST). Herein a novel steric locking strategy is proposed by incorporating methyl groups into D–A conjugated polymers. Benefitting from the methyl hindrance, the torsion between the donor and acceptor can be well tuned to form a sterically‐locked conformation, so that the unwanted relaxation toward planarity and thus conjugation elongation is prevented to boost hole–electron separation. The resultant D–A conjugated polymer achieves an extremely low ΔEST of 0.09 eV to enable efficient TADF. The corresponding doped and non‐doped devices are fabricated via a solution process, revealing a record‐high external quantum efficiency (EQE) of 24.0 % (79.4 cd A−1, 75.0 lm W−1) and 15.3 % (50.9 cd A−1, 47.3 lm W−1).

Precise Stepwise Synthesis of Donor-Acceptor Conjugated Polymer Brushes Grafted from Surfaces

“…Since their introduction in 1993 by the Havinga group [ 1 ], they have gained great interest as a particular example of conjugated polymers (CP). CPs are attractive for various photovoltaic or electronic applications [ 2 ] due to their unique electrical [ 3 ] and photophysical [ 4 ] properties, as well as their ease of processability [ 5 ], flexibility [ 6 ], low-cost [ 7 ] or a broad range of available architectures and chemical structures. One of the desired features of CP for such applications, typically provided by D-A polymers, is a low optical bandgap, which determines the efficient transport of charge carriers by promoting intramolecular charge transfer [ 8 ].…”

Design, synthesis, and properties of polystyrene‐based through‐space charge transfer polymers: Effect of triplet energy level of electron donor moiety on delayed fluorescence and electroluminescence performance

“…So far, TADF polymers are mainly focused on π‐conjugated D‐A architectures with feature of through‐bond charge transfer (TBCT) from covalently bonded donors and acceptors 12,13,20–32 . The introduction of donor and acceptor into conjugated polymer backbone not only allows to tune emission color by adjusting the donor and acceptor strength, but also can regulate energy levels of excited state to realize efficient exciton utilization.…”

“…[12][13][14][15][16][17][18][19] So far, TADF polymers are mainly focused on π-conjugated D-A architectures with feature of throughbond charge transfer (TBCT) from covalently bonded donors and acceptors. 12,13,[20][21][22][23][24][25][26][27][28][29][30][31][32] The introduction of donor and acceptor into conjugated polymer backbone not only allows to tune emission color by adjusting the donor and acceptor strength, but also can regulate energy levels of excited state to realize efficient exciton utilization. However, the strong electron coupling mediated by covalent bonds in TBCT polymers tends to induce considerable redshift of emission, undesirable for blue/deep blue emission.…”

Thermally Activated Delayed Fluorescent (TADF) Mono‐Polymeric OLED with Higher EQE over Its TADF Repeating Unit

“…[25][26][27][28] In this context, polymeric materials came on the stage by virtue of great film-forming ability and good thermal stability, which are quite suitable for solution-processed OLED. [29][30][31][32][33][34][35] However, the methodology of the TADF polymers is less developed, with most of the introduction of TADF units into the TADF polymers. Because intense TADF units tend to result in severly triplet-triplet annnihilation to reduce the efficiency, most TADF polymers need complicated structure to separate the TADF units, making the preparation more time consuming and laborious.…”