三聚芴分子玻璃的设计、合成与光电性能研究
摘要
在众多的电致发光材料中,一类具有无定形态性质的分子玻璃材料受到人们越来越多的关注。分子玻璃可以使用多种方法制备均匀、平整、稳定的薄膜,这样的薄膜可以显著的提高电致发光器件的性能,因此设计和合成适合电致发光的分子玻璃材料就显的极为重要。
本论文以芴的三聚体作为基本结构单元,通过取代基团刚柔性质的变化,构筑具有无定形态的分子玻璃材料。在具体的研究过程中,首先引入不同比例柔性的己基以改善螺环三聚芴由于强烈结晶所导致薄膜不稳定的问题。通过“刚柔并济”的分子设计得到无定形态的分子玻璃材料,它们的薄膜非常的平整并且稳定,在电致发光器件上表现了优异的性能。
为了得到具有更高稳定性的分子玻璃材料,并同时增加分子的空穴传输和注入能力,咔唑基团被引入三聚芴体系,合成了一系列具有烷基咔唑侧链的三聚芴分子。这类齐聚物保持了三聚芴体系优良的发光特性,而且表现了更稳定的无定形态性质。咔唑的引入降低了氧化电势,提高了HOMO能级,降低了空穴注入的势垒。由于这些齐聚物具有无定形态的性质,并且具有较高的分子量,它们的薄膜可以实现溶液旋涂加工。特殊的电化学聚合性质,使它们能够通过电化学聚合的方法得到了高发光效率的电沉积薄膜,这样的薄膜也可以用作电致发光器件的制备。
为了进一步提高三聚芴的发光效率和稳定性,刚性的联苯被引入这个体系,设计并合成了一系列具有螺芴三聚体为主链,烷氧基咔唑取代基团为侧链的齐聚物。这些齐聚物表现了更优异的发光性质,更重要的是芴9号碳上全芳香的取代基团增强了它们对光降解和热处理的抵抗能力。不过由于整个分子结构刚性的增强,使它们很难通过溶液加工形成平整的薄膜。进一步使用柔性的己基侧链取代刚性的联苯以后,这样的分子又可以通过溶液加工得到平整的薄膜,说明分子结构的刚柔性对成膜能力有着至关重要的影响。
Organic light-emitting diodes (OLED) have attracted great attentions of the science and industry fields because of their excellent performance. The molecular glasses with amorphous properties have attracted much attention in many electroluminescent materials. The molecular glasses were fabricated by various methods to gain homogeneous, uniform and stable films, which obviously enhance EL performance. Hence, it is very important that design and synthesis of molecular glasses suited LED devices.
Fluorene-based oligomers have attracted considerable attentions because they may be functional as model compounds for polyfluorenes (PFs). The oligomers with well-defined structure and excellent optoelectronic performance can reveal the research method of polymers and the relationships between structures and properties, and were used in electroluminescent devices and other optoelectronic devices. The fluorene trimer with spirobifluorene unit exhibited blue emitting with high quantum yields and excellent thermal stability. However, intense crystallization tendency of this compound may result in a quite rough surface of its thin film, because the flexible groups is absent in molecular structure. Aiming at restraining crystallization tendency, and keeping the excellent optical and thermo- properties, a series of fluorene-based trimers with different substitutes at C-9 of fluorene were synthesized, their photophysical, electrochemical, morphological and electroluminescent properties were carefully investigated.
Firstly, the flexible hexyl groups were introduced into molecular structure of fluorene trimers, and the four trimers with rigid aromatic substitutes and flexible alkyl substitutes were synthesized and characterized. These trimers with same photophysical properties exhibited blue emitting with high quantum yields in solution and films, respectively. The electrochemical analysis revealed that different substitutes have not effect on electronic structure. The power XRD and DSC analusis demonstrated that the morphologies of four trimers are found to largely depend on their substitute, from crystalline of full aromatic or full alkyl substituted trimers to amorphous glass of mixed aromatic and alkyl substituted trimers. Furthermore, the films of molecular glasses are very stable during thermal annealing. In blue LED of these trimers with CIE (x=0.16, y=0.07), maximum brightness is 800 cd m-2,maximum external quantum efficiency is 2.9% and. In white LED combined rubrene, the molecular glass T4 showed good white emitting with CIE (x=0.32, y=0.37) and excellent EL performance (maximum brightness is 9500 cd m-2 and maximum efficiency is 6.15 cd A-1). The results indicate the advantage of molecular glasses in OLEDs.
Secondly, in order to fabricate films by spin-coated method, carbazole groups were introduced into fluorene trimers as substitutes, and a series of fluorene-based trimers with peripheral carbazole functional alkyl-substitution were synthesized. These compounds showed optical properties similar to fluorene trimers and stable amorphous properties with high Tg (143°C). Through incorporating carbazole units, the first oxidation potential was significantly reduced and the HOMO energy level was heightened, indicating an increased hole inject ability of the new compounds. Due to they have amorphous properties and high molecular weight, the films can be fabricated by spin-coated method. Furthermore, after thermal annealing a smooth surface (Rms:0.215 nm) have less effect. The more efficient and deep blue OLED devices have been achieved by using spin-coating film as emitter. The carbazole can be easily oxidized and subsequently electropolymerized under relatively low potential, which has no effect on the compounds backbone. By electrochemical reactions between the carbazyl radical cation, their electrochemically deposited films with strong fluorescence were gained, which offered a method of grafting light-emitting materials onto substrates for LEDs fabrication, and such devices with rather high efficiency (0.72%) and luminance (4224 cd m-2) have been achieved.
Lastly, in order to more enhance luminescent efficiency and thermal stability, the rigid spirobifluorene units were introduced into molecular structure of fluorene trimers, and a novel series of fluorene trimers with spirobifluorene backbone and peripheral alkoxyl-substituted carbazole functional groups are synthesized. They exhibite excellent luminescent properties, in particular the efficiencies in films are above 80%. The aromatic substitutes on 9-position of fluorene can increase glass transition temperature and can effectively restrain the photodegradation. However, the smooth films were not gained by spin-coated method, and the films surface with rather roughness were observed even though using eyes. It is possible reason that the backbone has too rigid and the peripheral flexible alkyls were not enwind effectively resulting in enough glutinosity. Understanding relationship between molecular structure and film formed stability, the flexible hexyl groups were introduced as substitute instead of rigid spirobifluorene. By structural modification, this novel compound can form smooth film in the progress of spin-coated method, and OLED device were fabricated.
本论文以芴的三聚体作为基本结构单元,通过取代基团刚柔性质的变化,构筑具有无定形态的分子玻璃材料。在具体的研究过程中,首先引入不同比例柔性的己基以改善螺环三聚芴由于强烈结晶所导致薄膜不稳定的问题。通过“刚柔并济”的分子设计得到无定形态的分子玻璃材料,它们的薄膜非常的平整并且稳定,在电致发光器件上表现了优异的性能。
为了得到具有更高稳定性的分子玻璃材料,并同时增加分子的空穴传输和注入能力,咔唑基团被引入三聚芴体系,合成了一系列具有烷基咔唑侧链的三聚芴分子。这类齐聚物保持了三聚芴体系优良的发光特性,而且表现了更稳定的无定形态性质。咔唑的引入降低了氧化电势,提高了HOMO能级,降低了空穴注入的势垒。由于这些齐聚物具有无定形态的性质,并且具有较高的分子量,它们的薄膜可以实现溶液旋涂加工。特殊的电化学聚合性质,使它们能够通过电化学聚合的方法得到了高发光效率的电沉积薄膜,这样的薄膜也可以用作电致发光器件的制备。
为了进一步提高三聚芴的发光效率和稳定性,刚性的联苯被引入这个体系,设计并合成了一系列具有螺芴三聚体为主链,烷氧基咔唑取代基团为侧链的齐聚物。这些齐聚物表现了更优异的发光性质,更重要的是芴9号碳上全芳香的取代基团增强了它们对光降解和热处理的抵抗能力。不过由于整个分子结构刚性的增强,使它们很难通过溶液加工形成平整的薄膜。进一步使用柔性的己基侧链取代刚性的联苯以后,这样的分子又可以通过溶液加工得到平整的薄膜,说明分子结构的刚柔性对成膜能力有着至关重要的影响。
Organic light-emitting diodes (OLED) have attracted great attentions of the science and industry fields because of their excellent performance. The molecular glasses with amorphous properties have attracted much attention in many electroluminescent materials. The molecular glasses were fabricated by various methods to gain homogeneous, uniform and stable films, which obviously enhance EL performance. Hence, it is very important that design and synthesis of molecular glasses suited LED devices.
Fluorene-based oligomers have attracted considerable attentions because they may be functional as model compounds for polyfluorenes (PFs). The oligomers with well-defined structure and excellent optoelectronic performance can reveal the research method of polymers and the relationships between structures and properties, and were used in electroluminescent devices and other optoelectronic devices. The fluorene trimer with spirobifluorene unit exhibited blue emitting with high quantum yields and excellent thermal stability. However, intense crystallization tendency of this compound may result in a quite rough surface of its thin film, because the flexible groups is absent in molecular structure. Aiming at restraining crystallization tendency, and keeping the excellent optical and thermo- properties, a series of fluorene-based trimers with different substitutes at C-9 of fluorene were synthesized, their photophysical, electrochemical, morphological and electroluminescent properties were carefully investigated.
Firstly, the flexible hexyl groups were introduced into molecular structure of fluorene trimers, and the four trimers with rigid aromatic substitutes and flexible alkyl substitutes were synthesized and characterized. These trimers with same photophysical properties exhibited blue emitting with high quantum yields in solution and films, respectively. The electrochemical analysis revealed that different substitutes have not effect on electronic structure. The power XRD and DSC analusis demonstrated that the morphologies of four trimers are found to largely depend on their substitute, from crystalline of full aromatic or full alkyl substituted trimers to amorphous glass of mixed aromatic and alkyl substituted trimers. Furthermore, the films of molecular glasses are very stable during thermal annealing. In blue LED of these trimers with CIE (x=0.16, y=0.07), maximum brightness is 800 cd m-2,maximum external quantum efficiency is 2.9% and. In white LED combined rubrene, the molecular glass T4 showed good white emitting with CIE (x=0.32, y=0.37) and excellent EL performance (maximum brightness is 9500 cd m-2 and maximum efficiency is 6.15 cd A-1). The results indicate the advantage of molecular glasses in OLEDs.
Secondly, in order to fabricate films by spin-coated method, carbazole groups were introduced into fluorene trimers as substitutes, and a series of fluorene-based trimers with peripheral carbazole functional alkyl-substitution were synthesized. These compounds showed optical properties similar to fluorene trimers and stable amorphous properties with high Tg (143°C). Through incorporating carbazole units, the first oxidation potential was significantly reduced and the HOMO energy level was heightened, indicating an increased hole inject ability of the new compounds. Due to they have amorphous properties and high molecular weight, the films can be fabricated by spin-coated method. Furthermore, after thermal annealing a smooth surface (Rms:0.215 nm) have less effect. The more efficient and deep blue OLED devices have been achieved by using spin-coating film as emitter. The carbazole can be easily oxidized and subsequently electropolymerized under relatively low potential, which has no effect on the compounds backbone. By electrochemical reactions between the carbazyl radical cation, their electrochemically deposited films with strong fluorescence were gained, which offered a method of grafting light-emitting materials onto substrates for LEDs fabrication, and such devices with rather high efficiency (0.72%) and luminance (4224 cd m-2) have been achieved.
Lastly, in order to more enhance luminescent efficiency and thermal stability, the rigid spirobifluorene units were introduced into molecular structure of fluorene trimers, and a novel series of fluorene trimers with spirobifluorene backbone and peripheral alkoxyl-substituted carbazole functional groups are synthesized. They exhibite excellent luminescent properties, in particular the efficiencies in films are above 80%. The aromatic substitutes on 9-position of fluorene can increase glass transition temperature and can effectively restrain the photodegradation. However, the smooth films were not gained by spin-coated method, and the films surface with rather roughness were observed even though using eyes. It is possible reason that the backbone has too rigid and the peripheral flexible alkyls were not enwind effectively resulting in enough glutinosity. Understanding relationship between molecular structure and film formed stability, the flexible hexyl groups were introduced as substitute instead of rigid spirobifluorene. By structural modification, this novel compound can form smooth film in the progress of spin-coated method, and OLED device were fabricated.
引文
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