二氰基取代芳香共轭基团为受体构建热活化延迟荧光材料体系
发布时间：2019-06-12 20:01
【摘要】：基于热活化延迟荧光(TADF)机制的有机发光二极管(OLED)由于采用不含铱、铂等贵重金属的纯有机荧光材料,可以利用三重态到单重态的逆系间窜越(RISC)过程,实现100%的激子利用率,经过近几年的发展,TADF-OLED的器件外量子效率(EQE)已接近甚至超过磷光器件的水平。TADF材料不仅具有低成本的优势,同时其既可以作为发光材料也可以作为主体材料而实现多功能应用,已被视为下一代OLED材料而得到广泛研究,但目前还面临一些亟需解决的问题。一方面,红光TADF材料还很缺乏,其器件的性能也远远落后于蓝光和绿光TADF器件。红光TADF材料的设计合成和器件构筑对研究者来说仍然是一项充满挑战的工作。另一方面,TADF器件在高亮度或高电流密度下由于三重态-三重态激子或单重态-三重态激子湮灭等原因存在严重的效率滚降问题。因此,在TADF分子设计上,需要进一步拓展其材料体系,并详细研究其光物理机制,以期得到高性能和稳定的红光TADF材料。在器件构筑方面,需要开发新的器件结构和制备方法,深刻认识器件的物理过程,以期提高性能,改善寿命,最终实现产业化应用的高效稳定的TADF电致发光器件。本论文主要是以二氰基取代的芳香共轭衍生物作为受体基团构建新型的热活化延迟荧光材料体系,重点开展了以下几方面的研究工作:1、在第二章中,我们通过简单的反应合成了基于二氰基取代菲并吡嗪(DCPP)受体和三苯胺给体的D-π-A-π-D型的近红外TADF材料。理论计算表明其HOMO/LUMO分布方式具有大部分分离的特征,有利于得到小的单重态-三重态能级差(ΔEST≈0.20 e V)。另外,HOMO/LUMO在DCPP受体核上还有小部分重叠,有利于获得较高的振子强度(f≈0.1508),以增强辐射跃迁速率。因此,这种分子设计可以同时获得小的ΔEST和高的辐射跃迁速率。其非掺杂薄膜光谱发射峰位为708 nm,荧光量子效率为14%,在近红外荧光化合物处于较高水平。我们首次制备了近红外发光的TADF器件。其中非掺杂器件最大EQE达2.1%,CIE坐标为(0.70,0.29)。掺杂器件发光峰位为668 nm,最大外量子效率达9.6%,接近一些类似光谱的近红外磷光OLED的水平。此项研究工作为开发高效的近红外TADF材料提供了一些设计思路。2、在第三章中,我们研究了不同给体基团对TADF材料性质的影响。我们通过在DCPP受体核上,连接不同给体取代基团如咔唑(Cz)、二苯胺(DPA)和二甲基吖啶(DMAC),合成了三个D-A-D型的TADF化合物。采用苯环作为π-桥,合成了另外两个D-π-A-π-D型TADF化合物。这些化合物实现了黄光至深红光的发射。其中以DMAC为给体的化合物具有最大的D-A扭曲角,其表现了较小的ΔEST和短的延迟荧光寿命。采用双极性分子为主体制备了黄光至深红光发射的TADF器件。其中黄光器件效率可达47.6 cd A~(-1)(14.8%),橙光器件效率可达34.5 cd A~(-1)(16.9%),深红光器件效率可达13.2 cd A~(-1)(15.1%)。然而以Cz和DPA为给体的化合物作为发光层的器件由于大的ΔEST和长的延迟荧光寿命导致了显著的效率滚降。因此设计红光TADF分子时,除了确保高的荧光量子效率外,还应进一步减小ΔEST和延迟荧光寿命来降低激子淬灭,从而得到低效率滚降的器件。3、在第四章中,为了调控TADF分子的发光波长,使其进一步红移,我们通过拓展DCPP受体核的π共轭,使受体核的吸电子能力增加、LUMO能级降低,实现了这一目的。通过连接二苯胺(DPA)或二甲基吖啶(DMAC)作为给体基团,我们得到了两个红光至近红外的TADF化合物。理论计算的能级轨道分布表明,拓展DCPP受体核的π共轭后,分子的LUMO能级降低了0.25~0.28 e V,而HOMO能级基本不变,因此禁带降低,光谱红移。两个化合物的非掺杂薄膜光谱峰位均为765 nm,相比于第二章的化合物红移近60 nm。其中以DPA为给体的分子制备的掺杂OLED器件,发光峰位在708 nm,最大EQE为5.4%,为目前报道的荧光近红外器件的最高效率之一。这一结果表明,延长受体核的π共轭长度以及增加其吸电子能力是实现红光至近红外TADF发射的有效策略。4、在第五章中,我们采用二氰基取代的绿光TADF材料4Cz IPN作为敏化主体材料,喹吖啶酮衍生物作为客体掺杂剂,利用逆系间窜越(RISC)和F?rster能量转移(FRET)过程,使在TADF主体上产生的三重态激子能量能被传统荧光材料捕获,有效提高了荧光器件的激子利用率。基于此策略制备的OLED器件最大EQE和功率效率分别达到14.6%和53.4 lm W-1,高于传统荧光型OLED器件的最大效率值近三倍。并且由于主客体之间的快速能量转移使主体上的三重态激子密度降低,器件的效率滚降很小,在亮度为1000 cd m-2下,EQE仍能为13.7%。这种方法不仅提高了传统荧光OLED的效率,而且有助于获得低效率滚降和高色纯度的TADF电致发光器件。综上所述,我们设计合成了一系列基于二氰基取代芳香共轭受体的黄光至近红外光TADF材料,并系统研究了材料结构与物理性质的关系,进一步拓展和丰富了红光TADF材料体系;在器件构筑上,我们采用二氰基取代的TADF材料作为传统荧光材料的敏化主体,基于能量转移过程,实现了效率远超传统荧光器件的高效率且低滚降的电致发光器件,对进一步开发高效的热活化延迟荧光材料与器件体系起到了积极的促进作用。
[Abstract]:The organic light-emitting diode (OLED) based on the heat-activated delayed fluorescence (TADF) mechanism can realize 100% exciton utilization by using a pure organic fluorescent material containing noble metals such as platinum and platinum, In recent years, the external quantum efficiency (EQE) of the TADF-OLED has been close to or even higher than that of the phosphorescent device. The TADF material not only has the advantage of low cost, but also can be used as a light-emitting material and can be used as a main material to realize the multi-function application, and has been regarded as the next-generation OLED material to be widely researched. In one aspect, that red TADF material is also scarce, and the performance of the device is well behind the blue and green TADF devices. The design and synthesis of the red TADF material and the construction of the device remain a challenging task for the researchers. On the other hand, the TADF device has serious efficiency roll-down problems due to triplet-triplet exciton or singlet-triplet exciton annihilation at high brightness or high current density. Therefore, in the design of the TADF molecule, it is necessary to further expand its material system, and to study its optical physical mechanism in detail with a view to obtaining high-performance and stable red-light TADF material. In the aspect of device construction, a new device structure and a preparation method are needed, and the physical process of the device is deeply realized, so that the performance is improved, the service life is improved, and the highly efficient and stable TADF electroluminescence device of the industrial application is finally realized. The thesis mainly focuses on the following aspects:1. In the second chapter, A near-infrared TADF material based on dicyano-substituted phenanthrene (DCPP) receptor and triphenylamine donor was synthesized by a simple reaction. The theoretical calculation shows that the HOMO/ LUMO distribution mode has a large part of the separation characteristics, and is favorable for obtaining the small singlet-triplet energy level difference (CREST-0.20e V). In addition, the HOMO/ LUMO has small partial overlap on the core of the DCPP receptor, which is favorable for obtaining higher transducer intensity (f = 0.1508) to enhance the radiation transition rate. Thus, such a molecular design can simultaneously obtain a small CREST and a high radiation transition rate. Its non-doped thin-film spectral emission peak is 708 nm, the fluorescence quantum efficiency is 14%, and the near-infrared fluorescent compound is at a higher level. For the first time, a near-infrared light-emitting TADF device was prepared. In which the maximum EQE of the non-doped device is 2.1% and the CIE coordinates are (0.70, 0.29). The emission peak of the doped device is 668 nm, the maximum external quantum efficiency is up to 9.6%, and the level of the near-infrared phosphorescent OLED similar to the spectrum is close to. This study provides some design considerations for the development of an efficient near-infrared TADF material. In chapter 3, we have studied the effects of different donor groups on the properties of the TADF material. Three D-A-D-type TADF compounds were synthesized by connecting different donor substituent groups, such as Cz, diphenylamine (DPA), and dimethyl disulfide (DMAC) on the DCPP receptor core. Two additional D-A-A-1-D-type TADF compounds were synthesized by using a benzene ring as a 1-bridge. These compounds achieve the emission of yellow to deep red light. In which the compound with dmac as the donor has the greatest d-a twist angle, which exhibits a small bEST and a short delay fluorescence lifetime. TADF devices with yellow to deep red light are prepared by using bipolar molecules as the main body. The efficiency of the yellow light device can reach 47.6 cd A-(-1) (14.8%), the efficiency of the orange-light device can reach 34.5 cd A-(-1) (16.9%), and the efficiency of the deep red light device can reach 13.2 cd A-(-1) (15.1%). However, the device taking Cz and DPA as the donor as the light-emitting layer resulted in significant efficiency roll-off due to large ESTs and long delayed fluorescence lifetime. Therefore, in designing the red TADF molecule, in addition to ensuring high fluorescence quantum efficiency, the exciton quenching can be further reduced by reducing the fluorescence lifetime of the TADF and the delay, so as to obtain a low-efficiency roll-off device. The purpose of this is to increase the electron-withdrawing ability of the receptor core and to decrease the LUMO level by expanding the cohomology of the nuclear of the DCPP receptor. By connecting diphenylamine (DPA) or dimethyl disulfide (DMAC) as a donor group, we obtained two red to near-infrared TADF compounds. The energy level orbit distribution of the theoretical calculation shows that the LUMO level of the molecule is reduced by 0.25-0.28e V, while the HOMO energy level is substantially unchanged, so that the forbidden band is reduced and the spectrum is red shifted. The spectral peak of the non-doped thin film of the two compounds was 765 nm, and the red shift of the compound in the second chapter was nearly 60 nm. The light-emitting peak is at 708nm and the maximum EQE is 5.4%, which is one of the highest efficiency of the currently reported fluorescent near-infrared device. The results of this study show that the effective strategy for the emission of red-to-near-infrared TADF is the extension of the cohomology length of the receptor core and the increase of its electron-absorption ability. In the fifth chapter, we use the green TADF material 4Cz IPN which is a two-cyano-substituted green-green TADF as the sensitizing main material. The energy of the triplet exciton generated on the main body of the TADF can be captured by the conventional fluorescent material, and the exciton utilization rate of the fluorescent device can be effectively improved. The maximum EQE and power efficiency of the OLED device prepared based on this strategy reach 14.6% and 53.4 lm W-1, respectively, which is nearly three times higher than the maximum efficiency value of the conventional fluorescent OLED device. And due to the rapid energy transfer between the main objects, the triplet exciton density on the main body is reduced, the efficiency of the device is small, and the EQE can still be 13.7 percent under the brightness of 1000 cd-2. The method not only improves the efficiency of the conventional fluorescent OLED, but also helps to obtain a TADF electroluminescent device with low efficiency and high color purity. In conclusion, we have designed a series of yellow-to-near-infrared (TADF) materials based on dicyano-substituted aromatic co-organic receptors, and systematically studied the relationship between the structure and physical properties of the materials, and further developed and enriched the red-light TADF material system; on the device construction, By adopting the TADF material substituted by the dicyano as the sensitizing main body of the traditional fluorescent material, the invention realizes the high-efficiency and low-roll-down electroluminescent device with the efficiency and the ultra-conventional fluorescent device based on the energy transfer process, And has a positive effect on the further development of the high-efficiency heat-activation delayed fluorescent material and the device system.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ422
本文编号：2498266
[Abstract]:The organic light-emitting diode (OLED) based on the heat-activated delayed fluorescence (TADF) mechanism can realize 100% exciton utilization by using a pure organic fluorescent material containing noble metals such as platinum and platinum, In recent years, the external quantum efficiency (EQE) of the TADF-OLED has been close to or even higher than that of the phosphorescent device. The TADF material not only has the advantage of low cost, but also can be used as a light-emitting material and can be used as a main material to realize the multi-function application, and has been regarded as the next-generation OLED material to be widely researched. In one aspect, that red TADF material is also scarce, and the performance of the device is well behind the blue and green TADF devices. The design and synthesis of the red TADF material and the construction of the device remain a challenging task for the researchers. On the other hand, the TADF device has serious efficiency roll-down problems due to triplet-triplet exciton or singlet-triplet exciton annihilation at high brightness or high current density. Therefore, in the design of the TADF molecule, it is necessary to further expand its material system, and to study its optical physical mechanism in detail with a view to obtaining high-performance and stable red-light TADF material. In the aspect of device construction, a new device structure and a preparation method are needed, and the physical process of the device is deeply realized, so that the performance is improved, the service life is improved, and the highly efficient and stable TADF electroluminescence device of the industrial application is finally realized. The thesis mainly focuses on the following aspects:1. In the second chapter, A near-infrared TADF material based on dicyano-substituted phenanthrene (DCPP) receptor and triphenylamine donor was synthesized by a simple reaction. The theoretical calculation shows that the HOMO/ LUMO distribution mode has a large part of the separation characteristics, and is favorable for obtaining the small singlet-triplet energy level difference (CREST-0.20e V). In addition, the HOMO/ LUMO has small partial overlap on the core of the DCPP receptor, which is favorable for obtaining higher transducer intensity (f = 0.1508) to enhance the radiation transition rate. Thus, such a molecular design can simultaneously obtain a small CREST and a high radiation transition rate. Its non-doped thin-film spectral emission peak is 708 nm, the fluorescence quantum efficiency is 14%, and the near-infrared fluorescent compound is at a higher level. For the first time, a near-infrared light-emitting TADF device was prepared. In which the maximum EQE of the non-doped device is 2.1% and the CIE coordinates are (0.70, 0.29). The emission peak of the doped device is 668 nm, the maximum external quantum efficiency is up to 9.6%, and the level of the near-infrared phosphorescent OLED similar to the spectrum is close to. This study provides some design considerations for the development of an efficient near-infrared TADF material. In chapter 3, we have studied the effects of different donor groups on the properties of the TADF material. Three D-A-D-type TADF compounds were synthesized by connecting different donor substituent groups, such as Cz, diphenylamine (DPA), and dimethyl disulfide (DMAC) on the DCPP receptor core. Two additional D-A-A-1-D-type TADF compounds were synthesized by using a benzene ring as a 1-bridge. These compounds achieve the emission of yellow to deep red light. In which the compound with dmac as the donor has the greatest d-a twist angle, which exhibits a small bEST and a short delay fluorescence lifetime. TADF devices with yellow to deep red light are prepared by using bipolar molecules as the main body. The efficiency of the yellow light device can reach 47.6 cd A-(-1) (14.8%), the efficiency of the orange-light device can reach 34.5 cd A-(-1) (16.9%), and the efficiency of the deep red light device can reach 13.2 cd A-(-1) (15.1%). However, the device taking Cz and DPA as the donor as the light-emitting layer resulted in significant efficiency roll-off due to large ESTs and long delayed fluorescence lifetime. Therefore, in designing the red TADF molecule, in addition to ensuring high fluorescence quantum efficiency, the exciton quenching can be further reduced by reducing the fluorescence lifetime of the TADF and the delay, so as to obtain a low-efficiency roll-off device. The purpose of this is to increase the electron-withdrawing ability of the receptor core and to decrease the LUMO level by expanding the cohomology of the nuclear of the DCPP receptor. By connecting diphenylamine (DPA) or dimethyl disulfide (DMAC) as a donor group, we obtained two red to near-infrared TADF compounds. The energy level orbit distribution of the theoretical calculation shows that the LUMO level of the molecule is reduced by 0.25-0.28e V, while the HOMO energy level is substantially unchanged, so that the forbidden band is reduced and the spectrum is red shifted. The spectral peak of the non-doped thin film of the two compounds was 765 nm, and the red shift of the compound in the second chapter was nearly 60 nm. The light-emitting peak is at 708nm and the maximum EQE is 5.4%, which is one of the highest efficiency of the currently reported fluorescent near-infrared device. The results of this study show that the effective strategy for the emission of red-to-near-infrared TADF is the extension of the cohomology length of the receptor core and the increase of its electron-absorption ability. In the fifth chapter, we use the green TADF material 4Cz IPN which is a two-cyano-substituted green-green TADF as the sensitizing main material. The energy of the triplet exciton generated on the main body of the TADF can be captured by the conventional fluorescent material, and the exciton utilization rate of the fluorescent device can be effectively improved. The maximum EQE and power efficiency of the OLED device prepared based on this strategy reach 14.6% and 53.4 lm W-1, respectively, which is nearly three times higher than the maximum efficiency value of the conventional fluorescent OLED device. And due to the rapid energy transfer between the main objects, the triplet exciton density on the main body is reduced, the efficiency of the device is small, and the EQE can still be 13.7 percent under the brightness of 1000 cd-2. The method not only improves the efficiency of the conventional fluorescent OLED, but also helps to obtain a TADF electroluminescent device with low efficiency and high color purity. In conclusion, we have designed a series of yellow-to-near-infrared (TADF) materials based on dicyano-substituted aromatic co-organic receptors, and systematically studied the relationship between the structure and physical properties of the materials, and further developed and enriched the red-light TADF material system; on the device construction, By adopting the TADF material substituted by the dicyano as the sensitizing main body of the traditional fluorescent material, the invention realizes the high-efficiency and low-roll-down electroluminescent device with the efficiency and the ultra-conventional fluorescent device based on the energy transfer process, And has a positive effect on the further development of the high-efficiency heat-activation delayed fluorescent material and the device system.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ422
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