【作者】 王鑫；

【导师】 张红星；

【作者基本信息】 吉林大学 ， 物理化学， 2019， 博士

【摘要】 锌卟啉及其衍生物具有特殊的结构、优良的光物理和光化学性质,在有机电致发光二极管、染料敏化太阳能电池、催化及光动力治疗等领域有着广泛的应用。利用各种化学手段对锌卟啉衍生物的分子结构进行修饰,能够有效地调节其光电化学性质。目前报道的关于锌卟啉配合物的修饰主要是在其外围meso和β位上,这样的修饰策略一般都能够保持锌卟啉的平面性,并且能够增加其共轭程度。而相对于平面锌卟啉衍生物,非平面锌卟啉衍生物的结构和性质方面的研究却鲜有报道。本论文采用量子化学方法对具有不同π共轭结构和不同芳香性的非平面锌卟啉配合物进行了理论模拟研究,计算了此类配合物与光电功能相关的基态及激发态性质,阐述了非平面锌卟啉配合物分子结构和分子性能之间的关系,为设计、合成新型的光电功能材料提供了理论依据。研究工作主要包括以下三方面的内容:1.锌卟啉的一个次甲基桥键断裂可将平面锌卟啉转变为扭曲的“开环”锌卟啉。在此,我们使用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)方法分析并对比了平面“闭环”锌卟啉和非平面“开环”锌卟啉配合物的几何结构,前线分子轨道性质、吸收光谱性质及发射光谱性质,探讨了开环对锌卟啉电子结构及激发态性质的影响机制。与“闭环”锌卟啉相比,“开环”锌卟啉中的四个吡咯基不再共平面,其两个最低非占据轨道不再简并,两个最高占据轨道之间的能量差也有明显增大。这使“开环”锌卟啉配合物的Q带吸收光谱和最低能荧光发射光谱都发生了红移并且强度增强。同时,与“闭环”锌卟啉相比,非平面“开环”锌卟啉配合物具有更大的柔性和相对较大的斯托克斯位移。希望我们的研究结果能够对将来设计新型锌卟啉类光电材料提供参考。2.结合TD-DFT计算和Gouterman四轨道模型理论对一系列四吡咯锌配合物的特殊分子结构和光谱性质进行了较系统的研究,预测了π-共轭效应对四吡咯锌体系的几何结构、前线分子轨道的分布和组成及吸收跃迁性质的影响机制。理论研究结果表明,随着锌卟啉的共轭结构被打破,三联吡咯锌配合物,二联吡咯锌配合物和单吡咯锌配合物的分子结构由平面变成了扭曲的四面体结构。同时,随着锌卟啉π共轭程度的降低,其前线分子轨道(HOMO-1,HOMO,LUMO和LUMO+1)不再与其它分子轨道在能量上相互分离,且未占据轨道中的金属成分会随之增多。此外,锌卟啉π共轭结构被破坏后,其电子吸收光谱涉及到更多轨道间的电子跃迁,最终导致其Q带和B带吸收吸收呈现出先增强后减弱和逐渐减弱的趋势。研究该类四吡咯锌配合物分子结构与光谱性质之间的关系有助于人们深入理解Gouterman四轨道理论,并为实验合成有效、可控、稳定的吡咯锌配合物提供理论基础和线索。3.基于实验已合成的非平面五元吡咯锌配合物,通过改变五元吡咯配体的结构及芳香性,采用DFT和TD-DFT方法设计研究了一系列可用于光动力治疗的五元吡咯锌光敏剂。结果表明,将参考化合物中的非芳香性配体替换为芳香性配体后,其稳定性显著增加。并且,增加配体的芳香性还有利于降低参考化合物的电子亲和能,提高参考化合物的自旋轨道耦合常数及最低三重激发态能量,进而有利于提高了此类配合物作为光敏剂的光动力治疗活性。希望此研究能够为实验上改进和设计新型高效五元吡咯锌光敏材料提供有价值的参考。更多还原

【Abstract】 Zinc porphyrins and their derivatives have been widely applied in organic light emitting diodes,dye-sensitized solar cells,catalysis and photodynamic therapy due to their special structures,excellent photophysical properties and photochemical properties.Moreover,the photoelectrochemical properties of zinc porphyrin derivatives can be effectively adjusted by modifying their molecular structures with various chemical methods.At present,the modification of zinc porphyrin complexes is mainly at their meso and β sites.Generally,such modification strategies can increase the conjugation degree and maintain the planarity of zinc porphyrin.However,compared with planar zinc porphyrin derivatives,the structures and properties of non-planar zinc porphyrin derivatives have rarely been reported.In this paper,a series of nonplanar zinc porphyrin complexes with different π-conjugated structures and different aromaticity were theoretical investigated by using quantum chemical method.The ground state and excited state properties related to photoelectric functions were calculated.Meantime,the relationship between molecular structures and molecular properties of these nonplanar zinc porphyrin complexes were studied,which could provide theoretical basis for the design and synthesis of novel photoelectric functional materials.This work mainly includes the following three aspects.1.Exploring the relationship between the geometrical structures and spectral properties has great significance to design some desirable materials.For important pyrrole contained macromolecules,there is a new complex of Zn tetrapyrrin with opened chain ligand derived from breaking one methine bridged of Zn porphyrin,named as open-ring Zn porphyrin.Density functional theory(DFT)and time-dependent density functional theory(TD-DFT)are used to analyze the geometrical structure,frontier molecular orbital properties,absorption spectra and emission spectra for the open-ring zinc porphyrin complexes.Comparing to the closed-ring zinc porphyrin complexes,the four pyrrole groups in the open-ring zinc porphyrin are no longer coplanar,the HOMOs and LUMOs are no longer degenerate,the lowest lying absorption and emission start to increase in intensity with the shifting of charge transfer transition band to near-infrared region.Moreover,compared with the closed-ring zinc porphyrin,the open-ring zinc porphyrin complex has a relatively large Stokes shift due to its greater flexibility.We hope these theoretical studies will assist the design of novel molecular materials.2.The special molecular structures and spectra properties of a series of different π-conjugation tetrap yrrole zinc complexes are systematically studied based on TD-DFT calculations and four-orbital model theory.The π-conjugation effects on the geometrical structures and absorption spectra properties are predicted.The calculated results show that breaking the conjugate structure of zinc porphyrin,the molecular structures of these tetra pyrrole zinc complexes can be changed from planar structure to distorted tetrahedral structure.At the same time,the frontier molecular orbitals(HOMO-1,HOMO,LUMO and LUMO+1)of these tetra pyrrole zinc complexes are no longer separated from other molecular orbitals in energy,the orbital with metal distribution is approaching to lowest unoccupied molecular orbital(LUMO),and the absorption spectra is no longer weak at Q-like band and no longer intense at B-like band with the breakdown of the π-conjugation of zinc porphyrins.Studying the relationship between the molecular structure and spectral properties of these tetra pyrrole zinc complexes will help people better understand Gouterman’s four-orbital theory.Moreover,we hope this study can provide theoretical basis and clues for the experimental synthesis of effective and stable zinc pyrrole complexes.3.The purpose of this work described herein is to design highly efficient photosensitizers(PS)for photodynamic therapy(PDT)in theory.A series of expanded Zn porphyrins have been studied as light activated PS.Their main photophysical properties are systematically calculated by using density functional theory and its time-dependent extension.The mechanisms of PDT are discussed.All the considered candidates exhibit intense absorption in the therapeutic window,efficient intersystem crossing,and sufficient energy for singlet molecular oxygen production.Accordingly,the designed Zn pentaphyrins and sapphyrins would be proposed as potential PS for PDT.Moreover,the therapeutic effects of Zn pentaphyrins and sapphyrins are better than those of the referenced Zn iso-pentaphyrin.It is expected that the results could provide a new way to design and develop PS for PDT application.更多还原