【作者】 白福全；

【导师】 张红星；

【作者基本信息】 吉林大学 ， 物理化学， 2009， 博士

【摘要】 过渡金属配合物作为功能材料应用于通讯、信息、显示等许多领域,是当前国际上的一个研究热点。过渡金属配合物的吸收发射电子转移一般与金属中心原子的d轨道-电子到金属或配体的s/p-轨道或s/p-轨道的电荷转移有关,电子吸收在紫外区而电子发射在可见区的可能性较大,是可见区发光材料的上佳选择。理论研究过渡金属配合物激发态性质是实验研究的有力补充,其优点是独立性、前瞻性和经济性。在本文中,我们综述了Pt(II)配合物的实验研究背景、理论发展现状以及本文研究的理论和实际意义。总结以往理论方法和计算经验,研究了几类铂配合物的基态和最低能激发态的几何结构、激发态势能面以及吸收发射光谱等性质。通过对结构-性质之间关系的探索,为功能材料的发展提供理论支持。主要内容有一下几方面:(1)通过含时密度泛函方法(TD-DFT)计算了一系列基于碳联非对称二亚胺配体的Pt(II)配合物的电子结构和光谱性质。使用密度泛函方法(DFT)和单电子激发组态相互作用(CIS)分别对基态和激发态电子结构进行优化。光谱研究结果表明:这类配合物的最低能吸收具有1,3MLCT/1,3ILCT混合电荷转移跃迁特点。与吡唑配体无取代基配合物比较,吡唑片段引入吸电子基团(-CF3; -C3F7)使配合物最低能吸收蓝移,反之给电基团(-Me; -tBu)等的引入使得配合物最低能吸收发生红移。当共轭配体骨架引入N杂原子,配体共轭作用增强。MO能量改变的结果使配合物最低能电荷跃迁的能级发生变化,同样导致了光谱的移动。基于配体的不对称性和边界轨道特征可通过取代基效应和杂原子效应来调整等特点,总结了配合物低能电荷跃迁的特点。取代基变化影响配合物跃迁能大约0.3 eV,而N杂原子影响配合物跃迁能大约0.4 eV。(2)利用DFT和TD-DFT方法对Pt(II)σ-炔基低聚物重复单元骨架为基础合成的一类配合物进行激发态特征量子化学计算。讨论了配合物基态和激发态的结构,电子性质,电子亲合能和电离势等结果。配合物的最低能吸收具有LLCT结合MLCT跃迁特征。比起单核配合物,相应双核配合物最低能吸收的振子强度有显著的增强,这是因为双核配合物增强的非局域化作用和更加平面化的分子几何。计算得出配合物在CH2Cl2溶剂中磷光发射为配合物的最低能吸收跃迁的逆过程,当分子增强了电子局域化效应和伴随的三态溶剂相互作用时,自身具有了3[π*?π]/3MLCT跃迁特征。另外,此配合物具有较大的第一超极化率(β0)值,可做为潜在非线性光学材料应用。其中的双核类配合物因为拥有较大的跃迁距和较小的跃迁能而使得β0值相对于单核配合物在更高的水平上。(3)利用开壳层和闭壳层DFT方法和TD-DFT方法对铂N杂卡宾(NHC)配合物的几何构型,电子态结构以及光学性质进行计算,着眼于配合物激发态的寿命和量子效率的分子本质原因展开研究。利用开壳层密度泛函方法优化[Pt(meim)2]2+, [Pt(meim)(cyim)]2+和[Pt(cyim)2]2+的d-d三重激发态几何构型。综合利用基态激发态势能面理论定性研究得出同系列配合物取代基对激发态能级的影响。密度泛函方法分析表明,配合物量子效率变低是因为配体场影响分子T1态和d-d态间的能垒的降低,更小的结构形变和弱化的体系d-d重组能。更多还原

【Abstract】 As functional materials, transition metal complexes materials have become a fascinating field in the world for their diverse potential applications in communication, information, and flat-panel displays, and their absorption and emission transitions usually are related to the charge transfer between d orbitals of metal and s/p orbitals of metal or ligand. Because such an electronic absorption in the ultraviolet region usually conducts the corresponding emission in the visible region, transition metal complexes are one of the most excellent candidates to serve as visible-region optical material. Theoretical studies on the excited state properties of transition metal complexes are the strong complement for experimental investigation. The electronic absorption and emission of molecules are complicated microscopic processes between the ground- and excited-state transitions. With the development of quantum chemistry and computational technique, especially the successful application of density functional method, the electronic structures and properties of molecules in the ground state have been fully understood in theory and widely applied in chemistry. However, the studies on the excited-state properties still remain infant and excited states themselves are related to many photoelectric phenomena in the modern chemistry and physics. Therefore, quantum chemistry related to the electronic excited states should be one of the most major research directions in the future. The advantages of theoretical study are retrenchment, indicative of theoretical forward looking and independence.The electronic excited states of molecules have higher energy and unsteady characteristics, which easily emit the energy to recur the steady ground state in a short time. So it is difficult for experiment to obtain reliable information about the excited states of molecules. Theoretical chemists attempt various electronic structure theories of excited states to seek the method that can accurately predict excited-state electronic structures and be applied in the calculations of relatively large molecules without consuming excess computational resources. So far, CIS (Single excitation configuration interaction), unrestricted DFT and TD-DFT (Time-dependent density functional theory) methods have been widely used to treat the electronic excited states of large molecular systems. It has been established that the solvents affect the luminescence of complexes. Many theoretical methods were employed to treat properties of complexes in solution. The first strategy puts the attention on the microscopic interactions of the solute with a limited number of solvent molecules; the whole system (the“supermolecule”) is studied with quantum mechanical methods usually employed for single molecules, and the effects of specific solute-solvent interactions are brought in evidence. An increasing number of solvent molecules can be added to this model, thus gaining supplementary (and detailed) information about solvent effects. The second strategy tries to directly introduce statistically averaged information on the solvent effect by replacing the microscopic description of the solvent with a macroscopic continuum medium with suitable properties (dielectric constant, thermal expansion coefficient etc.). Recently, QM/MM (Quantum mechanical and molecular mechanical) method has been developed to account for the solvent effects.In this paper, combining the benefits of various quantum chemical computational methods and considering the solvent effects, we systematically studied on the ground- and excited-state conformations, excited state potential energy curves (PEC), absorption and emission spectra of several kind of platinum complexes. Through the exploration between structure and property, it can help to improve the performance of the functional materials. The following is the main results:1. Electronic structures and spectroscopic properties of a series of platinum(II) complexes based on C-linked asymmetrical diimine ligand have been studied by the time-dependent density functional theory (TD?DFT) calculations. The ground- and excited-state structures were optimized by the DFT and single-excitation configuration interaction (CIS) methods, respectively. The calculated structures and spectroscopic properties are in agreement with the corresponding experimental results. The results of the spectroscopic investigations revealed that the lowest-energy absorptions have 1,3MLCT/1,3ILCT mixing characters. When the electron-withdrawing groups (-CF3, 1a1; -C3F7, 1a2) are introduced into the pyrazolate fragment, the lowest-energy absorptions are blue-shifted compared to that without substituents on the pyrazolate fragment, while the opposite case is observed for the electron-donating groups (-Me, 1a3; -tBu, 1a4). The conjugation of the C-linked diimine ligand is enhanced through introducing more N heteroatoms into this segment. As a results of MO energy change, the lowest-energy absorptions are blue-shifted in the order 1 < 1b1 < 1b2. With the replacement of pyridyl by pyrazine, the HOMO energy of 1b3 is comparable to 1, but the LUMO energy is decreased by 0.8 eV, and the lowest-energy absorptions are red-shifted to 2.36 eV. Otherwise, the phosphorescent emissions of these complexes have the 3MLCT/3ILCT character, and should be originated from the lowest-energy absorptions. When the pyrazolate fragment is replaced by the indazole group(1a6), the HOMO and LUMO orbitals of the pyridyl-indazolate ligand platinum(II) complexes have obviousπandπ* orbital characters. Therefore, there is no evident MLCT character in the lowest energy absorption and emission.2. We report a combinational DFT and TD-DFT study of the electronic and optical properties of several tridentate cyclometalated mononuclear [Pt(C^N^N)(C≡CR)] (1-3), [Pt(C^N^N)(C≡CRC≡CH)] (4), and dinuclear [Pt(C^N^N)(C≡CRC≡C)Pt(C^N^N)] (5 (C2 symmetry) and 5′(Cs symmetry)) platinum(II) complexes withσ-acetylide ligand bearing fluorene substituents, where HC^N^N = 6-aryl-2,2’-bipyridine, R = fluorene-2,7-diyl 1, 4, 5 and 5′, R = 9,9-dimethylfluorene-2,7-diyl 2, R = 9,9-diethylfluorene-2,7-diyl 3. The structural and electronic properties of the ground- and lowest triplet state and the EA and IP values of the complexes are discussed. It is found that all of the lowest-lying absorptions are categorized as the LLCT combined with the MLCT transitions. The oscillator strengths of the lowest energy absorptions get a remarkable enhancement for the dinuclear complexes 5 and 5′compared to 1-4 due to the increase of electronic delocalization on the more planar molecular geometry. In general, the phosphorescent emissions of these complexes in CH2Cl2 are the reverse process of their lowest energy absorption transitions, except that of 4 is assigned as 3[π* ?π]/3MLCT transition because of the strengthened electronic localization effect and the interaction with the solvent in the lowest triplet state. In addition, these complexes hold promise as a new kind of nonlinear optical material owing to their large static first hyperpolarizabilities (β0). Theβ0 value has increased in the dinuclear complexes in contrast to those of the mononuclear ones owing to their larger transition moment and smaller transition energy.3. We present a full density functional theory (DFT) and time-dependent density theory (TDDFT) investigation of the geometry, electronic structures, and optical properties of N-heterocyclic platinum(II) tetracarbene complexes aiming at providing a definitive characterization of the photophysical properties of this system. Density functional analysis show that the absorption spectra and emission wavelengths of [Pt(meim)2]2+, [Pt(meim)(cyim)]2+, and [Pt(cyim)2]2+ are analogical, and the reason of a significantly decrease in quantum efficiency for [Pt(cyim)2]2+ is which reaches the nonradiative deactivation dd excited state with lower thermal barrier in contrast with [Pt(meim)2]2+.The results presented here demonstrate that photophysical properties, in particular excited-state lifetimes, can be strongly affected by ligands. Access to such information is fundamental for a rational design of new metal complexes with tunable photochemical features. Combining photophysical measurements with emerging capabilities to investigate excited-state potential energy surfaces using quantum chemical calculations is seen to offer in-depth information about such effects. Only a correct description of orbital energies and shapes, and a full comprehension of the role played by different excited states in light-induced electronic transitions, can guide the introduction of advantageous structural changes on photoactivable metal species.更多还原