基于手性三蝶烯的红光热激活延迟荧光聚合物及其有机发光二极管研究★

doi:10.6023/A23040153

摘要/Abstract

手性三蝶烯并吖啶(TpAc)具有独特的三维结构、同共轭效应和两个分离的反应位点. 采用手性给体-受体(D*-A)共聚的设计策略, 以TpAc作为电子给体与强电子受体4,7-二溴苯并[c][1,2,5]噻二唑(BTZ)直接偶联聚合, 得到了非共轭型手性红光热激活延迟荧光(TADF)聚合物(R,R)-/(S,S)-pTpAcBTZ. 所得聚合物最高占据分子轨道(HOMO)和最低未占分子轨道(LUMO)有效分离并获得小的ΔE_ST (0.08 eV), 具有显著的红光TADF性质(λ_toluene=663 nm). 同时聚合物显示出镜像的红光圆偏振发光(CPL)信号, 其|g_lum|值约为1.4×10^-3. 通过溶液旋涂法制备了红光发光二极管(OLEDs), 所得器件最大发射峰为658 nm, 其在1.0 cd/m²的亮度下开启电压为3.6 V, 最大外量子效率为2.0%. 该非共轭型手性聚合物的设计和红光TADF性能有利于促进手性发光材料及电致红光器件等相关研究领域的发展.

关键词: 热激活延迟荧光, 圆偏振发光, 聚合物, 三蝶烯, 红光

Chiral triptycene acridine (TpAc) has unique 3D structure, homoconjugation effect and two separate reaction sites. By using the design strategy of chiral electron donor-acceptor (D*-A) copolymerization, the triptycene-based non-conjugated chiral red thermally activated delayed fluorescence (TADF) polymers (R,R)-pTpAcBTZ and (S,S)- pTpAcBTZ were directly polymerized by using TpAC as chiral electron donor and 4,7-dibromobenzo[c][1,2,5]thiadiazole (BTZ) as the strong electron acceptor. The molecular weights of these chiral polymers were characterized by gel permeation chromatography (GPC), and the GPC analysis indicated that the number-average molecular weight (M_n) ranged from 37.9 kDa to 39.3 kDa with the polydispersity index (PDI) values from 1.99 to 2.02. The chiral polymers exhibited good solubility in common organic solvents, such as chlorobenzene, tetrahydrofuran, dichloromethane and chloroform, ensuring good film quality during solution processing. In addition, the chiral TADF polymers showed excellent thermal stability with thermal decomposition temperature (T_d) (corresponding to a 5% weight loss) around 440 ℃, and glass transition temperatures (T_g) were also detected in these chiral polymers when they were heated to 300 ℃, which could be ascribed to their highly rigid and twisted structures. According to the onset of the oxidation curve, the highest occupied molecular orbital (HOMO) energy levels of the chiral polymers were estimated to be -5.27 eV. Their corresponding optical energy band gaps were estimated to be 2.21 eV from the onset of their ultraviolet-visible (UV-Vis) absorption spectra in toluene. Consequently, the corresponding lowest unoccupied molecular orbital (LUMO) energy levels were calculated to be -3.06 eV. The S₁ and T₁ values of pTpAcBTZ were 2.13 eV and 2.05 eV, respectively, which were determined at 77 K, and the corresponding ΔE_ST was 0.08 eV which were favorable for reverse intersystem crossing of excitons from T₁ to S₁ states. The chiral TADF polymers showed efficient red TADF (λ_toluene=663 nm) activity, and they also displayed mirror-image red circularly polarized luminescence (CPL) signals, with the |g_lum| of approximately 1.4×10^-3. By using the chiral red polymers as emitters, the obtained solution-processed red OLEDs displayed maximum electroluminescence peak of about 658 nm, and its turn-on voltage is 3.6 V at a brightness of 1.0 cd/m². The device exhibited well device efficiency, with a maximum external quantum efficiency of 2.0%, maximum current efficiency of 1.1 cd/A, maximum power efficiency of 0.8 lm/W. The design of the non-conjugated chiral polymers and their red TADF activity are conducive to promoting the development of related research fields such as chiral luminescent materials and red luminescence devices.

Key words: thermally activated delayed fluorescence, circularly polarized luminescence, polymer, triptycene, red luminescence

引用此文

王银凤, 李猛, 陈传峰. 基于手性三蝶烯的红光热激活延迟荧光聚合物及其有机发光二极管研究^★[J]. 化学学报, 2023, 81(6): 588-594.

Yinfeng Wang, Meng Li, Chuanfeng Chen. Chiral Triptycene-Based Red Thermally Activated Delayed Fluorescence Polymers and Their Organic Light-Emitting Diodes^★[J]. Acta Chimica Sinica, 2023, 81(6): 588-594.

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图/表 8

图1. 基于手性三蝶烯红光TADF聚合物的设计策略与化学结构

Figure 1. Design strategy and chemical structure of red TADF polymers based on chiral triptycene

图式1. 聚合物(R,R)-pTpAcBTZ和(S,S)-pTpAcBTZ的合成路线

Scheme 1. Synthetic route of polymers (R,R)-pTpAcBTZ and (S,S)-pTpAcBTZ

图2. pTpAcBTZ的(a) LUMO和(b) HOMO电子云分布

Figure 2. (a) LUMO and (b) HOMO electron cloud distribution of pTpAcBTZ

图3. (R,R)-pTpAcBTZ在不同溶剂中的(a)吸收光谱和(b)发射光谱(λex=500 nm)、(c)在77 K时, (R,R)-pTpAcBTZ (w=15%)掺杂的mCP薄膜的PL光谱(λex=500 nm)和(d) (R,R)-/(S,S)-pTpAcBTZ在掺杂膜下的瞬态PL光谱(λem=660 nm, τIRF≈1 μs)

Figure 3. (a) UV-Vis absorption and (b) PL spectra of (R,R)-pTpAcBTZ in different solvents (λex=500 nm), (c) PL spectra at 77 K in (R,R)-pTpAcBTZ (w=15%) doped mCP (λex=500 nm) and (d) transient PL spectra of (R,R)-/(S,S)-pTpAcBTZ in doped films (λem=660 nm, τIRF≈1 μs)

图4. (R,R)-/(S,S)-pTpAcBTZ的(a) CD和(b) CPL光谱

Figure 4. (a) CD and (b) CPLspectra of (R,R)-/(S,S)-pTpAcBTZ

图5. OLEDs中使用的材料的能级图和分子结构

Figure 5. Energy level diagram and molecular structures of the materials employed in OLEDs

图6. 基于(R,R)-/(S,S)-pTpAcBTZ的OLEDs的(a)EL光谱和(b) EQE-电流密度特性、基于(R,R)-pTpAcBTZ的OLEDs (c)电流密度-电压-亮度特性和(d)电流效率-电流密度-功率效率特性以及基于(S,S)-pTpAcBTZ的OLEDs (e)电流密度-电压-亮度特性和(f)电流效率-电流密度-功率效率特性

Figure 6. (a) EL spectra and (b) EQE-density characteristics of (R,R)-/(S,S)-pTpAcBTZ-based OLEDs, (c) current density-voltage-luminance and (d) current efficiency-current density-power efficiency characteristics of (R,R)-pTpAcBTZ-based OLEDs, and (e) current density-voltage-luminance and (f) current efficiency-current density-power efficiency characteristics of (S,S)-pTpAcBTZ-based OLEDs

Device^a	V_T^b/V	λ_EL^c/nm	EQE_max^d/%	CE_max^e/(cd•A^-1)	PE_max^f/(lm•W^-1)	L_max^g/(cd•m^-2)
A	3.6	658	2.0	1.1	0.8	1058
B	3.5	658	1.8	1.0	0.8	949

表1. 基于(R,R)-/(S,S)-pTpAcBTZ的OLEDs器件性能

Table 1. Device performances of OLEDs based on (R,R)-/(S,S)-pTpAcBTZ

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