【作者】 解增旗；

【导师】 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】 有机单晶是热力学上稳定的分子堆积形态,具有高度有序的分子堆积结构,而且杂质含量极低,通常表现出较高的迁移率;同时单晶中明确的分子构型与分子排列可以为研究分子间作用力、分子排列方式对固态发光效率、载流子迁移率等物理性质的影响规律提供理想的模型。所以近几年有机单晶材料与器件成为一个新的研究热点,这方面的研究也必将从更深层次上揭示有机光电材料中的基本物理过程。反式二苯乙烯基苯是聚苯撑乙烯类化合物中结构最简单、也最典型的模型化合物,研究其衍生物的分子堆积结构与光电性能之间的关系不仅可以指导设计高性能的聚合物光电材料,而且本身也可以成为优良的晶体光电材料。本论文立足于一类苯基取代的二苯乙烯基苯衍生物,详细讨论了它们的分子堆积结构与光电性能,主要内容如下:1.合成了一系列苯基取代二苯乙烯基苯的衍生物,合成过程中发现在某些Wittig反应中可以很方便地获得纯的顺式产物,将其进一步处理可以得到纯的反式产物。2.反式二苯乙烯基苯主链上引入苯基取代基可以有效的抑制平行的分子堆积模式,诱导产生其它有利于实现高晶态发光效率的分子堆积模式,如交叉分子偶极堆积(X-堆积)和错位平行分子偶极堆积(J-堆积)。3.错位平行分子偶极堆积有利于高晶态发光效率,在这样的晶体中构筑强的分子间π-π相互作用可以有效地增加晶体中的载流子迁移率,从而实现一个晶体中高发光效率与高迁移率的统一。4.严重扭曲的分子结构一直以来被认为是不利于发光的,如顺式双键曾经被作为聚苯撑乙烯化合物中的缺陷结构;我们对顺式苯基取代二苯乙烯基苯的研究发现晶体中分子间相互作用可以有效地稳定分子激发态,从而增强发光。更多还原

【Abstract】 In recent years, the investigations of optoelectronic functional organic crystals have been paid great attention in the field of organic optoelectronic materials. Compared with amorphous thin film materials, organic single crystals have the characteristics of high stability, high ordered structure, and high carrier mobility, which make them attractive candidates for optoelectronic devices. Single crystal with definite structure provides a model for us to investigate the basic intermolecular interactions (supramolecular interaction), and the relationship between molecular stacking modes and optoelectronic performance (luminescence and carrier mobility).trans-Distyrylbenzene (trans-DSB) is one of the simple and typical model compound for poly(p-phenylene vinylene) (PPV) type materials, which has been widely used in polymeric light-emitting diodes. trans-DSB has deep blue emission in dilute solution with very high photoluminescence efficiency nearly up to 100%; while in solid state (film or crystal), the emission spectrum is red-shifted and the quantum efficiency decreased dramatically (<10%). In the crystal, trans-DSB molecules tend to pack with parallel stacking image, in which the‘H-stacking’is formed for the transition dipole direction is along the molecular long axis. In the H-aggregate, the inter dipole interaction induce the energy level of the lowest excited state splitting into two energy levels, and the lower one is optically forbidden. After the molecule in H-aggregate absorbs a photo and get to the excited state, it will relax to the lowest energy level rapidly, which make the H-aggregate has very low quantum efficiency. The emission spectrum is red shifted because the 0-0 transition is forbidden based on the parallel inter dipole interaction. However, in some other molecular dipole stacking mode, such as J-aggregate, the lowest splitting energy level due to the inter dipole interaction is optically allowed. Thus the emission spectrum is red shifted, and the photoluminescence efficiency is very high. There is also another molecular dipole stacking mode that is called as‘X-aggregate’, in which the inter dipole interaction is very weak. The emission properties of the X-aggregate are similar to the dilute solution and of course the quantum efficiency is very high.The molecular dipole stacking in the crystal of trans-DSB is H-stacking, which is deficient for luminescence efficiency. It is possible to get highly efficient crystalline materials by adjusting the molecular dipole stacking mode. Based on this information, we added phenyl substituents on the backbone of trans-DSB to avoid the parallel molecular stacking, and furthermore to induce multi- molecular stacking modes.During the synthesis of diphenyl-distyrylbenzene using Wittig reaction, we accidentally found that the phenyl substituents make the reaction have highly stereo-isomer selection and the cis-isomer is nearly up to 100%. After we deposit the result solution into methanol, the pure cis-compound can be obtained easily. The pure trans-isomer can be prepared by reflux the p-xylene solution of cis- isomer using a little iodine as catalyzer. We studied the structural and physical properties of the cis- and trans-compounds, and found that the differences between then are similar to the most cis- and trans- isomers.The crystal structures of the cis- and trans-compounds were examined in detail. The trans-DPDSB (2,5-diphenyl-1,4-distyrylbenzene with two trans double bonds) tends to form two different polymorphs under different conditions, which have X-stacking and J-stacking respectively. The two polymorphs have very high photoluminescence efficiency. The value for X-stacking crystal is up to 80% and the value for J-stacking crystal is 48%.Strong intermolecularπ-πinteractions are benefit for charge transport between adjacent molecules. Although X-stacking is very good for high photoluminescence efficiency, it is deficient for charge transport because the intermolecularπ-overlap is small. While in J-stacking, it is easy to form strong intermolecularπ-πinteractions, and then it is possible to combine high luminescence efficiency and high charge-carrier mobility in one crystal. In the single crystal of trans-DFPDSB (2,5-di-(3,5-difluoro-phenyl)-1,4-distyrylbenzene with two trans double bonds), there is strongπ-πinteractions and the molecular dipole stacking is typical J-stacking. The photoluminescence efficiency of the trans-DFPDSB crystal is 49%, and the calculated hole mobility is 0.88 cm2/Vs.In the cis-DPDSB (2,5-diphenyl-1,4-distyrylbenzene with two cis double bonds) crystals, it is impossible to form face-to-face parallel molecular stacking for the torsional molecular conformations. Three different polymorphs of cis-DPDSB can be formed with the assistant of C-H···πinteractions. cis-DPDSB has very low quantum efficiency in solution due to the occurrence of the photochemical processes; while in crystal the efficiency is as high as 50%, which can be attributed to the stabilized excited state by intermolecular interactions.更多还原