【作者】 孙刚；

【导师】 苏忠民；

【作者基本信息】 东北师范大学 ， 物理化学， 2005， 硕士

【摘要】 1987 年美国 Kodak 公司的 C. W. Tang 等人以 Alq3作为发光层,TPD 做空穴传输层,采用真空蒸镀的方法,首次成功的制备了高效的绿色电致发光器件。此后,Alq3 就一直是科学界研究的热点问题,许多理论和实验工作者通过改变配体以及中心金属原子改变其发光性质。1990 年,英国剑桥大学的 R. Friend 等人将聚苯撑乙烯（PPV）的预聚体制成薄膜,在真空干燥下转化成 PPV 薄膜,成功地制备了单层结构的聚合物电致发光器件。由于聚合物材料的制作工艺、稳定性以及化学修饰性都比有机小分子更为优越,所以聚合物 PPV 以及 PPV 衍生物材料的研究进一步地推动了有机电致发光薄膜的研究,使之成为新的研究热点。 随着科技的发展,理论工作者对复杂的大分子体系的电子结构的兴趣越来越浓,比如说蛋白质,有机聚合物等。通常从头算和半经验方法只对小分子或中等分子的体系在计算上可以实现,因为计算机时与体系大小的指数呈线形关系:tcup∝N^x （tcup 表示计算机时,N 是电子轨道数量,X 通常是大于 1 的数值）。为了发展大分子体系的光学性质的计算,香港大学的陈冠华教授在线性标度基础上发展了量子化学计算方法定域密度矩阵方法（LDM）。它是通过将原子的价电子轨道定域在原子周围,观察轨道上电子的密度变化,来分析电子的性质的一种方法。 本文在第三章采用定域密度矩阵方法对含有 8 羟基喹啉或 Alq₃的 PPV 聚合物的分子在光谱结构,前线分子轨道,以及定域密度矩阵和共轭性质等的电子性质方面对其激发态进行了研究。在第四章用同样的方法研究了 2-（2’-吡啶基）苯并咪唑衍生物及其铍配合物的电子跃迁性质。 第三章主要结论如下: 1.体系的前线分子轨道,吸收光谱和定域密度矩阵对于激发态的电子性质的表现是一致的。按照 PPV-Alq₃,PPV-hydro 和 PPV 的排列顺序,最大吸收峰依次红移。 2.对于主要讨论的 PPV-Alq₃ 分子,当外电场在 3.00eV,峰出现在 413nm,大约是在紫光区,在 Alq₃ 上的非主链的 8 羟基喹啉并未参与电子跃迁过程。而在 5.225eV下,出现了一个与其它分子不同的来自支链的 8 羟基喹啉在 237nm 的特征峰。说明了该分子的设计很有意义。 3.随后通过延长分子的 π 电子的共轭长度在 LDM 方法下研究电子的性质, PPV-hydro3 拥有最低的能带在 2.77eV,发光范围在 447nm 附近,在蓝光区。 第四章主要结论如下: 1.通过简单增加 bmbp 中间的苯环来增加体系的共轭长度,尽管可以使吸收峰红移,但改变了苯并咪唑的发光机理, 2-（2’-吡啶基）苯并咪唑在发光中并不起到明显的作用。 2.通过 π-π 堆积将两个分子 bmbp 堆积在一起研究发光性质,比较堆积后的吸收更多还原

【Abstract】 Electroluminescence （EL） study in small molecules and polymer materials will become more and more important in next generation technologies. They attract considerable interests in experiment and theory. Alq₃ is considered as a very typical small molecule in organic light-emitting diodes （OLED） experiments since the first realization of a multilayered EL device by Tang and VanSlyke in 1987. Its emission spectra were considered from the parts of ligands. Thus its academic investigations are discussed, for example some substitutional groups were joined on the 8-hydroxyquinoline or Al was replace by others metalsEL from π-conjugation organic polymers has lately been attracting a great deal of attention for academic interests as well as industrial interests since the Cambridge group’s report in 1990 on the EL properties of PPV. PPV has been studied extensively due to their high fluorescent yield and stability. Current research is concerned about changing substitute of PPV chain to obtain perfect emission spectra or improving illuminant intension and efficiency But the obstacle lies in the rapid increasing of computational costs as the systems become larger and more complex. The computational time tCPU is proportional to certain power of the system size, i.e., tCPU∝ Nx, where N is the number of electrons, and x is an exponent which is usually larger than 1. For instance, the computational time of ab initio Hartree-Fock （HF） molecular orbital calculation has an O (N³⁴) scaling. The localized density matrix theory （LDM） had been developed by G. H. Chen group. LDM method is the linear-scaling quantum chemistry method by simulating molecular excited state properties, such as optical, electric and magnetic properties, even in the large molecular systems. The method based on the time-dependent Hartree-Fock （TDHF） approximation which includes all single electron excitations and partial double, triple and the other multiple electron excitations15 and “the nearsightedness of equilibrium systems” Electronic properties of polymerized Alq₃ and 8-hyroxyquinoline linked with PPV units were characterized by LDM method in chapter 3. In chapter 4, electronic properties of transition of 2-（2’-Pyridyl） benzimidazole Derivative and their Be complexes were investigated with the same method. The main conclusions of chapter 3 are in the following: （I）The results from the FMOs, the absorption spectrum and density matrices are generally coherent. The largest absorption spectrum appears as red shift from the 8-hydroxyquinoline, PPV-Alq3, PPV-hydro to PPV （II）For mainly discussed PPV-Alq₃, absorption peak is about 3.00 eV, i.e. 413 nm near the purple light. Two 8-hydroxyquinolines have very slight effect on electronic transition. （III）With the increasing of length extension of molecule and π-conjugation, the first absorption peak shown red shift. Among the molecules PPV linked with Alq3 units, PPV-hydro3 possesses lowest energy gap is 2.77 eV, i.e.447nm near the blue light. The main conclusions of chapter 4 are in the following: （I） Although the absorption peaks show red shift through adding the benzene between the 2-（2’-Pyridyl） benzimidazole of two sides, but it change luminescence principle of pmbp. 2-（2’-Pyridyl） benzimidazole would not have contribution of electronic transition. （II） Comparing with the first absorption peak of bmbp2, that of the new molecule that is from two bmbp molecules through π-π stack appear 2nm red shift. It comes from the interaction between two different 2-（2’-Pyridyl） benzimidazole. （III） For two mainly discussed Be-2-（2’-pyri） benzimid and Be-bmb, Be-bmb has excellent property of luminescence. It is 436nm in the blue region. Electronic transition is between the Be-2-（2’-pyri） benzimid on one side and two benzenes coordinating with Be on the same side.更多还原