【作者】 何凤；

【导师】 沈家骢； 马於光；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2007， 博士

【摘要】 在过去的二十年中,有机小分子材料已被人们广泛地应用于电致发光器件的研究中,这些小分子材料由于其易获得高纯度的样品、化学结构容易调节等优点,在有机电致发光中显示了很好的应用前景。不过这些物质在固态中往往具有强结晶性,其通过真空蒸镀得到的无定形薄膜不是很稳定,从而大大影响相应电致发光器件的性能。基于对有机小分子材料的改性,本论文利用特殊的分子设计(十字交叉的多取代联苯中心)来调控苯撑乙烯齐聚物材料的形貌,逐步实现由晶态向无定形态的转变,并且同时考虑对分子刚性柔性的调节,使其更利于制备高效率的有机电致发光器件。基于联苯中心的十字交叉苯撑乙烯类齐聚物由于空间伸展的分子构型,其形貌逐渐转变为完全无定形态,而且由于分子内存在的交叉偶极排布,这类物质都具有高的固态发光效率;同时联苯中心还赋予这些分子部分的柔性,苯撑乙烯主链又具有很好的刚性,因此该类齐聚物材料兼具分子刚性柔性,是一类“刚柔并济”的特殊分子体系,可根据外界环境相应微调分子构型,使其在电致发光中有利于形成致密的薄膜材料。基于上述特点,本论文的工作主要包括以下几个方面:第一,通过制备基于联苯中心的齐聚物TSB和三联苯中心的齐聚物HSTP,成功实现了从其模型化合物DSB的强结晶态逐渐向无定形态的转变,并且在此基础上合成了具有不同取代基的系列苯撑乙烯齐聚物;第二,这类材料都能很好的应用于有机电致发光器件的研究,其中基于完全无定形态的齐聚物HSTP的电致发光器件显示了强烈的蓝色发光,器件流明效率为4.88 cd/A,达到了当前蓝色荧光小分子器件的最好水平;第三,基于这类物质的高固态发光效率和良好的成膜性,齐聚物DPA-TSB显示了954 GM的固态双光子发射截面,相对于其线性模型化合物DPA-DSB具有将近6倍的增加,有利于下一步这些材料在固态双光子荧光器件中的运用;第四,基于中心联吡啶官能化的十字交叉齐聚物bpy-DPA-TSB,成功将磷光金属铼配合物引入到该十字交叉苯撑乙烯齐聚物体系中,形成空间多维的给受体型分子,基于该金属磷光十字交叉苯撑乙烯齐聚物,在初步的光伏器件研究中得到了0.8 %的能量转换效率。更多还原

【Abstract】 π-Conjugated organic polymers have attracted considerable attention owing to their interesting properties as materials for charge transport, for non linear optics, for electronics and optoelectronics. Since the first poly(phenylenevineneyl) (PPV) materials was reported by the research group in Cambridge, PPV oligomers as their model compounds and as active materials themselves have induced great interest. Typically, distyrylbenzene (DSB) and its derivatives are widely investigated, which results in an increased understanding of the important conjugated polymers; meanwhile DSB is also a bright pure blue emitter. However, unfortunately, the excellent luminescent properties of DSB (ca. photoluminescence (PL) efficiency over 90 %) are only obtained in dilute solution, but in the solid-state DSB emits very weakly. This solid-state fluorescence quenching behavior has been associated with the formation of intermolecular aggregates, especially the side-by-side arrangements known as H-aggregates. This means that the stacking of DSB molecules plays a determining role in the physical properties of these materials. In order to adjust the morphology and enhance the PL efficiency, we introduced the biphenyl core into the cruciform system and constructed a series of PPV cruciform oligomers with a 2,5,2′,5′-substituted biphenyl center. Through this chemical construction, a morphology change from a crystalline to amorphous glass has been realized in cruciform oligomers, which is desirable for OLED applications. Meanwhile, the biphenyl core, which is a relatively free rotation center, can provide proper flexibility to those cruciform molecules. Because of the big substituted groups at the meta- and ortho-position of the biphenyl, the rotation of the biphenyl will be partly depressed, which endows the molecular with appropriate rigid/flexible abilities. Thus during film-forming process, the molecular stacking induced repulsion can trigger the mild rotation of the arms in this kind of cruciform PPV oligomers along the biphenyl bond to adjust its conformation for compact stacking, which will benefit their film forming ability during vacuum deposition or solution spin coating. Base on those two points, the cruciform PPV oligomers with a biphenyl core is very suitable for the OLEDs applications, which can result in the high performance devices.Firstly, the cruciform TSB with a biphenyl center and HSTP with a terphenyl center have been synthesized. They both show very high PL efficiency in the solid-state (TSB: 19 %; HSTP: 47 %). As a comparison, their model linear compound, DSB, only shows a very low PL efficiency in the solid-state (8 %). In the further device fabrication, the devices based on those two materials both show strong blue emission, especially for HSTP based blue OLEDs show a luminescence efficiency about 4.88 cd/A, which is one of the best reported blue OLEDs. The cruciform oligomer TSB also shows larger loading ability to the guest molecules and it can be used as a blue host materials. In the experiment, the blue PPV oligomer DPA-DPDSB had been used as the corresponding guest material. The PL efficiency of DPA-DPDSB/ TSB guest/ host films arrive the high level of 80 %, which is approaching the PL efficiency of the guest DPA-DSB in dilute solution (82 %), indicating that the host TSB can sufficiently disperse the guest DPA-DSB with little aggregation. The organic light-emitting devices using DPA-DPDSB (4 wt.%) doped TSB as blue emitting layer show the maximum efficiency of 18.33 cd/A. Combining rigid backbone structure and mild flexible property, the cruciform host TSB exhibits large loading ability to the guest DPA-DPDSB, and they can form a‘solid solution’film and dramatically enhance the performance of the guest/host devices.In following experiment, the cruciform PPV oligomers with different functional groups and further optimize the properties of the materials. Some other applications, such as two-photon absorption, had also been extended. DPA-DSB is a well-known compound with large two-photon absorption section and strong fluorescence in solution, but its easy crystallization characteristic leads to the formation of incontinuous crystalline phases during vacuum-deposition process, which greatly limits its applications as solid-state device. We construct a cruciform dimer of DPA-DSB, named as DPA-TSB, which can efficiently suppress crystalline and intermolecular interaction. The neat solid of DPA-TSB shows strong green-blue fluorescence as excited by steady-state absorption as well as two-photon absorption. The solid of DPA-TSB exhibits a PL efficiency (ηsolid) of 29 % and a solid-state two-photon action cross section (δηsolid) of 954 GM, which is much higher than its model compound DPA-DSB (ηsolid = 16 % andδηsolid = 150 GM). Based on the high PL efficiency, good film-forming ability and strong two-photon absorption, DPA-TSB exhibits great superiority for applications in solid-state optical devices. Based on the cruciform oligomer (bpy-DPA-TSB) with a bipyridine functional group, the phosphorescent rhenium (I) complex had been introduced into the cruciform system, in which a donor-acceptor molecule had been formed and can be used in organic photovoltaic application. There are some advantages for this new phosphorescent cruciform oligomer bpy-DPA-TSB-Re. Firstly, the phosphorescent metal complex always has a long lifetime due to the nature of triplet state, thus the rate of charge separation may be faster than that of recombination in this kind of material, which may further enhance the carrier separation. Secondly, the incorporation of the transition metal complexes into the polymers backbone can broaden the absorption spectra of copolymers due to the newly generated MLCT (metal to ligand charge transfer) absorption band. As a result, the photovoltaic device based on bpy-DPA-TSB-Re showed power conversion efficiency about 0.8 % (blended with BCPM), which is an encouraging result for application of such molecular donor-acceptor ensembles to solar cells.更多还原