Narrowband Deep-Blue Multi-Resonance Induced Thermally Activated Delayed Fluorescence: Insights from the Theoretical Molecular Design

Abstract

Multi-resonance thermal activated delayed fluorescence (MR-TADF) has been promising with large oscillator strength and narrow full width at half maxima of luminescence, overcoming the compromise of emission intensity and energy criteria of traditional charge transfer TADF frameworks. However, there are still limited theoretical investigations on the excitation mechanism and systematic molecular manipulation of MR-TADF structures. We systematically study the highly localized excitation (LE) characteristics based on typical blue boron-nitrogen (BN) MR-TADF emitters and prove the potential triangular core with theoretical approaches. A design strategy by extending the planar π-conjugate core structure is proposed to enhance the multiple resonance effects. Moreover, several substituted groups are introduced to the designed core, achieving color-tunable functions with relatively small energy split and strong oscillator strength simultaneously. This work provides a theoretical direction for molecular design strategy and a series of potential candidates for highly efficient BN MR-TADF emitters.

Narrowband emission: organic thermally-activated delayed fluorescence materials and underlying mechanisms

“…The TDDFT approach, which has been validated in excited-state simulations of D-A type TADF emitters at low computational cost, was also performed to reveal the underlying mechanism of MR-TADF emitters. 24,25,29 Despite the great success of TDDFT studies in qualitatively evaluating the structure-property relationship of MR-TADF materials, this method exhibits significant overestimations in simulating the DE ST , which is a key factor in harvesting triplet excitons. 27,28 In contrast to TDDFT, some wavefunction-based methods, such as SCS-CC2 and STEOM-DLPNO-CCSD, have been verified to balance the desired accuracy of DE ST values and modest computational cost for MR-TADF emitters.…”

“…18–21 In addition, the computational explorations of MR-TADF emitters have also been actively developed following research in the literature. 22–29 In this review, the focus is on the rational molecular design strategies, structure–property relationships, and underlying mechanisms for achieving narrowband emission with emission color-tuning in the entire visible region. This was followed by highlights of computational explorations in recent years and major challenges for the practical application of MR-TADF emitters.…”

“…[18][19][20][21] In addition, the computational explorations of MR-TADF emitters have also been actively developed following research in the literature. [22][23][24][25][26][27][28][29] Fig. 1 Photophysical processes of TADF emission: absorption (Abs), fluorescence (FL), phosphorescence (PH), intersystem crossing (ISC), reverse intersystem crossing (RISC), and internal conversion (IC).…”

A sensitization strategy for highly efficient blue fluorescent organic light-emitting diodes

“…According to the spin statistics under electrical excitation, the recombination of holes and electrons injected into OLED active layers is expected to produce singlet and triplet excitons in a 25%:75% (1:3) ratio [10,[14][15][16]. Unfortunately, only the 25% singlet excitons are luminescent in fluorescent organic light-emitting diodes (FOLEDs) [17]. In contrast, thermally activated delayed fluorescence (TADF) emitters can obtain internal quantum efficiency (IQE) of nearly 100% via reverse intersystem crossing (RISC) based on an efficient triplet-to-singlet process, and has emerged as a promising alternative to the more traditional phosphorescence and conventional fluorescence [16,18,19].…”

Design, Synthesis and Electroluminescent Properties of Multiresonant Thermally Activated Delayed Fluorescence Materials Based on Tetrahydroquinoline

“…随后以 DABNA-1 为原型, Lee 等 [6] 通过在二苯胺的 4 位上引入叔丁基得到了 2,12-二叔丁基-5,9-双(4-(叔丁基)苯基)-5,9-二氢-5,9-二氮杂-13b-硼化萘并[3,2,1-de]蒽(t-DABNA), 增加了分子间距 从而减弱之间的相互作用使得器件的外量子效率(EQE) 相比 DABNA-1 得到了提升, 并且通过使用 TADF 敏化 器件让器件的寿命和效率滚降得到改善, 但同时也让发 光产生红移, 使该器件发光的 CIE 值与 BT.2020 的蓝光 标准相差较远. 此外还出现了一系列关于 MR-TADF 材 料及器件的研究, 使 MR-TADF 器件发光从蓝光扩展到 绿光甚至是紫外光、红光 [7][8][9][10][11][12][13][14][15][16] , 而且器件的性能不断得 到改善以期达到商业应用的标准 [17][18][19][20][21][22][23][24][25] . 但在更深蓝区域 的 MR-TADF 分子则较少被发掘 [26][27][28][29][30] , 且深蓝光 TADF 器件大部分都具有较短的器件寿命 [31][32][33][34][35][36] .…”