【作者】 许海；

【导师】 马於光； 杨兵；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2009， 博士

【摘要】 联苯是很多有机π-共轭聚合物/齐聚物的结构基元和连接载体,对有机共轭材料的光电性能起到了重要的作用,这主要与联苯的结构特点密切相关,因此无论是实验化学还是理论化学,联苯基元的结构与材料性能的关系都是一个重要的研究课题。本论文应用Gaussian03量子化学程序对联苯类有机共轭分子的构型与电子结构进行了深入地研究,揭示了联苯单元的刚性与柔性特征及其对有机π-共轭分子光电性质的影响。联苯的构象具有多样性,取代联苯的构象更加复杂。我们研究了对联苯构象影响较大的邻位二取代联苯的优势构象与旋转能垒随各类不同取代基的变化。结果表明,邻位取代基对联苯构象和旋转能垒的影响最大的因素是取代基的空间位阻作用,而取代基的吸、推电子能力及共轭作用的影响相对较小。联苯基元的优势构象使两个苯环间形成一定的交叉二面角,利用这个特点,通过联苯桥将平面的有机共轭分子连接起来,可以比较容易的构筑一类十字交叉的分子体系——聚对苯乙烯撑的齐聚物,理论计算的结果显示,这类分子具有交叉扭曲的空间结构,这样的结构有效的抑制了分子在形成固体时生色团之间平行的π-π堆积而引起的荧光猝灭作用,进而提高了发光效率。此外,理论研究还证实了进一步通过联苯桥键增加生色团的数目以实现对材料体系的拓展,是提高光电性能的有效手段。联苯键具有一定的柔性,可以在一定的范围内旋转,当这种旋转达到一定程度时,甚至可以引发化学反应,实验中我们就观察到了一类由此产生的环加成反应。通过理论计算我们发现,引起这类反应的重要原因之一就是联苯键相对自由的旋转使原本处于分子两侧的双键转至同侧,并在逐步靠近的过程中发生了环加成反应。强的空间位阻作用有时也会使联苯键表现出较强的刚性,例如在蒽分子中心苯环上直接偶联上苯单元形成的联苯键就表现出很强的刚性特征,联苯单元的扭转二面角接近90°,这与蒽分子中两侧苯环上的氢原子产生了较大的空间位阻作用有关。这类分子通常具有很好的光电性能,其原因之一就是生色团被正交构象的联苯单元有效的保护。更多还原

【Abstract】 Biphenyl is the important structural elements of multifariousπ-conjugated polymers. In the recent 20 years, many of the organic conjugated molecules which are composed of biphenyl units or biphenyl likeness has been designed and exploited, such as poly-p-phenylene (PPP), polyfluorene (PF), polythiophene (PTh), ladder-type poly-p-phenylene (LPPP) and so on. Theseπ-conjugated polymers and their oligomers are the important members of the organic photoelectric function materials. As the characterization of the molecular structures, the conformation of the biphenyl units put up significant effect including solid emitting efficiency, charge carrier transport property, molecular recognition and sensor. So the investigates on the relation between chemical structures and photoelectric properties of the biphenyl derivate conjugated molecules, especially for the conformational diversifications of the biphenyl units affect to material properties, have very important significance. As the basilica instrument for investigating the relation of material structures and properties, quantum chemistry technique has been widely applied to modern chemistry, material science and correlative fields. In this thesis, we have studied configurations and electronic structures of several kinds of biphenyl derivate conjugated molecules using Gaussian 03 quantum chemistry program package, especially discussed that the rigidity and flexibility of biphenyl unit impacted photoelectric properties and reactive action of the material system. In different surroundings and conditions, the conformations of biphenyl exhibit multiformities. The experimental data show that the torsional angle of biphenyl has about 44°in gas phase, it ascribe conjunct results both of complanate conjugation effect and crossed steric hindrance effect between the ortho position hydrogen. In the crystalline state, however, biphenyl is almost coplanar molecules, which is claimed to be the result of flexible single bond between the benzene rings circumvolving to be propitious to stacking. In solution, biphenyl is found twisted conformations 0～45°depending on different solvent and temperature and for a melt of biphenyl the dihedral angle is 32±4°.The substituent biphenyl has more complicated conformation compared with biphenyl and the structures of biphenyl unit and molecules properties are also different following the changes of substituent type, amount and position. Among these, the substituent position is the most important factor to affect the preponderant conformations and rotary energy barriers of the biphenyl unit. The investigation indicate that the substitutes at meta or para position of the biphenyl bond has slight impact for the conformation of biphenyl unit, while the ortho position substitutes will bring obvious action for the torsional angle and rotary energy barrier of the biphenyl unit. In addition, if the number of substituent varies, the conformation of biphenyl unit also differs and that the most representative system is ortho disubstituted biphenyl because these types of molecules can represent all kinds of effects between different groups. Therefore, we used several theories and calculative methods to investigate the mutative rules about the preponderant conformations and rotary energy barriers of ortho position disubstituted at ground and excited states. Then we discussed respectively pull, push electronic and conjugated substitutes to contribute the conformation of the biphenyl unit. The calculated results reveal that the most important impact factor to the preponderant conformations and rotary energy barriers in the orhto position disubstituted biphenyl is effective steric hindrance effect, while the pull, push electronic power and the conjugated function of the substituent groups are relatively piddling. At the same time, the different effective steric hindrance effect can make the biphenyl unit possess the difference of rigidity and flexibility. It has been forecast in theory that the properties of the dipoles across stacking (X aggregate) between the conjugated molecules are close to the single molecule, and its photoelectric properties in solid state excelled familiar parallel stacking (H aggregate) and interlaced stacking (J aggregate). However, there are usually stronger intermolecular repulsion and higher total energy in the X aggregate so that it can hardly be formed. Whereas, using the certain torsional angle between the two benzene rings in the biphenyl unit, the flat conjugated molecules could be bridging with biphenyl bond, and it can easier to build up a type of decussate molecules to form X aggregate material which can improve the photoelectric properties. Such as, the center benzene ring of a type of PPV oligomer 1,4-distyrylbenzene (DSB) connects together directly using biphenyl bond to conform the compound 2,5,2’,5’-Tetrastyrylbiphenyl (TSB). The experimental data show that TSB have a obviously higher fluorescence quantum efficiency (11%) in solid than DSB (5%). And then imported two biphenyl-bridges to get the compound 2,5,2’,5’,2’’,5’’-hexastyryl-[1,1’;4’,1’’]-terphenyl (HSTP) has a further improvement on solid state fluorescence quantum efficiency (32%). Meanwhile, thermal analysis confirms that from DSB to TSB, the solid aggregation change from crystal state to semi-crystal state, while for HSTP the solid is completely exhibit as amorphous state, which indicates better and better machinable ability during the process of prepared thin film. By theoretical calculations, TSB and HSTP are indicated a cross and twist configuration between the two neighboring DSB chains. In gas phase, the biphenyl units of TSB and HSTP can swing in a large range and the molecules present obvious flexibility characters. When the molecules of this type of cross and twist structure come into solid state, the distance between the two chromophores (DSB units) can be drawn away effectively, it can suppress the parallelπ-πstacking which quenching fluorescence for the light-emitting efficiency enhancing, as well as keeping the flexibility characters for filming. The calculations on the electronic structure, absorption and emission character of TSB and HSTP indicate the photoelectric properties of this type of PPV oligomers with biphenyl-bridge are all similar as DSB and the effect of each chromophore is limited. Over here, the results of theoretical calculation are coinciding with the experimental data. In addition, the theoretical investigations have also confirmed that increasing the biphenyl units to expand this type of bridging PPV oligomers system is an effective strategy to achieve the light-emitting efficiency improvement and processing properties melioration that have similar photophysical properties.The biphenyl units of the PPV oligomers with biphenyl-bridged have typical flexibility characters because of the total energy among the various conformations closer and the rotary energy barriers lower so that the biphenyl bond can be relatively free swing at room temperature conditions. While the swing achieves a certain degree, it can even trigger a chemical reaction. For example, in experiments we found that 2,5,2’,5’-tetra(4-N,N-diphenylamino)styrylbiphenyl (DPA-TSB) and its analogues could easily occur intramolecular [2+2] cycloaddition reaction at room temperature in the dark. This confirmed a good response on the biphenyl bond flexibility. The theoretical analysis and calculation show that the biphenyl bonds relatively free swing make the original further distance of the two active double bonds circumvolve to ipsilateral of the biphenyl bond a relatively closer distance at room temperature, so it is the key step to trigger such type of intramolecular double bonds [2+2] cycloaddition reaction. Further we carried out theoretical research for the reaction mechanism. As a result of the cycloaddition reaction can be completed in the dark and the products even show a typical stereospecific characters, which determines the reaction mechanism can only be thermal concerted process or two-step rapid reaction process. We respectively calculated the two possible mechanism in detail using quantum chemistry methods, the results show that the thermal concerted mechanism has a larger activity energy and occurs the reaction difficultly, while the two-step rapid reaction mechanism complete the process relatively easy. Therefore, we believe that this type of thermal [2+2] cycloaddition reaction is most likely based on the two-step rapid reaction mechanism.Sometimes the larger steric hindrance effect can also bring the biphenyl unit a very strong rigidity. Here we studied the central benzene ring of anthracene molecule directly couple benzene units to conform a series of anthracene derivatives: 9-(3’,5’-diphenylbiphenyl-4-yl)-10-(3,5-diphenylphenyl)anthracene (DPB-DPPA), 9,10-bis(3’,5’-diphenylbiphenyl-4-yl)anthracene (BDPBA), 4-(10-(3,5-diphenylphenyl) anthracen-9-yl)-N,N-diphenylaniline (TPA-DPPA) and 4-(10-(3’,5’-diphenylbiphenyl- 4-yl)anthracen-9-yl)-N,N-diphenylaniline (TPA-DPBA). In thus series of anthracene derivatives molecules, the torsional dihedral angle of biphenyl units are all confined to the vicinity of 90°smaller scope, the biphenyl bonds show a very strong rigidity because of the larger steric hindrance effect of hydrogen atoms on both sides of the benzene ring of anthracene molecules. Owing to the series of anthracene derivatives form orthogonal conformation, the conjugation between groups are interrupted and independent of each other, so all the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are localized in certain group. Herein the HOMO and LUMO of full-phenyl-substituted DPB-DPPA and BDPBA are localized in the anthracene unit; while the molecules coupled triphenyl amine groups TPA-DPPA and TPA-DPBA take place the HOMO and LUMO separation, that is, HOMO is located in triphenylamine unit and the LUMO in anthracene unit. The reason of such electronic structure formation is orthogonal molecule conformation to interrupt conjugation and the frontier molecular orbitals energy levels show the characters of their own conjugate unit. In the meanwhile, such series of molecules show very good photoelectric properties on solid fluorescence quantum efficiency and stability, and its essence is that the chromophore (anthracene unit) is effectively protected by peripheral groups of orthogonal biphenyl bond coupled. In addition, the calculations of reorganization energy show that these anthracene derivatives have a smaller reorganization energy of hole transport, so the rate of hole transport is faster than the electron transport. But relatively speaking, the derivatives introduced triphenylamine unit (TPA-DPPA and TPA-DPBA) have the balance on both kinds of charge transfer rate. Such change has played an important role to improve the light-emitting efficiency and stability of organic light-emitting diodes (OLED).更多还原