【作者】 王冰；

【导师】 方奇；

【作者基本信息】 山东大学 ， 无机化学， 2023， 博士

【摘要】 1991年,Zyss等将非偶极非中心对称的“八极子”模型引入有机非线性光学(NLO)领域,标志八极分子NLO研究的开端。在各种八极分子中,共轭连接桥和电子受体外围封端的研究较为成熟,而其真正的八极核心却仍局限于苯、均三嗪、三聚茚和三聚吲哚等,更高效的八极电子给体中心核亟待合成和研究。四聚吲哚(Tetraindole,即TTI)为S4对称的三维(3D)八极共轭体系,三聚吲哚(Triindole,即TI)为C3h对称的平面八极共轭体系,这两种八极分子逐渐引起非线性光学领域的研究兴趣。有机共轭分子的光电性质受多种结构因素的影响,本论文主要采用两种分子设计策略去提高八极分子的非线性光学效应:(1)在母核TTI/TI上引入吸电子基团去提高分子内电荷转移能力;(2)在母核TTI/TI基础上进行芳环融合去扩展π离域体系。本论文基于S4对称的八极分子TTI和C3h对称的八极分子TI,实现了三维/二维电荷转移体系和π扩展共轭体系八极核心的构建,并测定了部分化合物的晶体结构,研究了它们的线性光物理性质和非线性光学效应。主要研究内容和结论如下:1.三/二维电荷转移体系:合成、结构、NLO效应和空穴传输性质基于TTI和TI,在2-和3-位分别引入吸电子基团-CF3,合成了位置异构的TTI和TI 衍生物:TTI-2-CF3 vs TTI-3-CF3 和 TI-2-CF3 vs TI-3-CF3,成功构建 3D 电荷转移体系和2D平面电荷转移体系。晶体结构表明马鞍形TTI-2-CF3分子保持S4对称的八极结构,平面形TI-2-CF3和TI-3-CF3可视为准八极分子:理论优化构型具有C3对称性,偶极矩很小(分别0.195和0.154 Debye),偏离C3h对称性不多;由于晶体堆积中的相互作用,这两种分子略微偏离C3对称性。TI-2-CF3结晶为非中心对称空间群Pna21,粉末的倍频强度(SHG)比KDP(KH2PO4)高一个数量级。目标化合物的吸收和荧光光谱均发生明显红移,表明电荷转移体系初步构建;TI-2-CF3红移更为显著,理论二阶非线性系数和理论空穴迁移率均明显高于其位置异构体TI-3-CF3,表明此体系中2-取代位点优于3-取代位点。2.π共轭扩展的TTI及TI体系:合成、结构、NLO效应和线性光物理性质实现了四聚/三聚吲哚的π共轭扩展,合成了一系列大π共轭的四聚/三聚吲哚衍生物(TTIid vs TIid,s-TTIbt vs s-TIbt,a-TTIbt vs a-TIbt,TIph),构建了更高效的八极电子给体中心核。晶体结构表明,四聚体s-TTIbt仍为S4对称的马鞍型八极分子,空间群为P42/n。理论构型优化表明,三聚物TIid,s-TIbt,a-TIbt的分子点群为C3h。芳环稠合后,目标化合物的吸收和荧光光谱发生明显红移,表明成功的扩展了 π-共轭体系;反式异构体(a-TTIbt和a-TIbt)光谱红移大于相应的顺式异构体(s-TTIbt和s-TIbt)。三聚体的实测双光子吸收截面δ提升至母体TI的10-102倍,反式异构体a-TIbt的δ值为顺式异构体s-TIbt的2.7倍,TI的102倍。π共轭扩展后二阶NLO系数(β值)相对于母体TTI和TI均明显提升,a-TTIbt和a-TIbt的计算β值明显高于s-TTIbt和s-TIbt,β值分别为母体TTI和TI的2.1和4.2倍。理论计算和实测光谱一致地表明反式体a-TIbt的π-共轭程度大于顺式体s-TIbt,这是a-TIbt具有较好的NLO性质的结构原因。3.N-苯基取代芳环稠合三聚吲哚体系:合成、结构和线性光物理性质在N-H位置引入苯基合成了一系列N-苯基芳环稠合三聚吲哚(TIid-ph,s-TIbt-ph和a-TIbt-ph),明显提升了化合物稳定性,表现出优良的溶液和固态荧光发光性质。苯环的引入使其紫外和荧光光谱均明显红移,表明N原子位置苯环对分子整体的共轭也有所贡献。s-TIbt-ph晶体中存在一定的位阻,分子失去严格平面性,N原子位置苯基之外的其它原子仍基本上保持共面,N原子上的苯环分别偏向分子平面的两侧。综上所述,我们采取了三种思路合成四聚吲哚和三聚吲哚衍生物,来调控目标化合物的光物理性质。对其晶体结构、溶液/固态发光进行测试研究,从理论和实验上对其非线性光学响应(倍频和双光子吸收)展开了研究,对部分化合物电荷传输性质进行理论研究,并结合理论计算分析了异构体性质差异的原因。本文基于环聚吲哚构建了非线性光学响应更强的八极分子核心,为将来构建高效非线性光学材料和其他光电功能材料奠定了基础。更多还原

【Abstract】 Since 1991,the concept of "octupole" has been introduced into the field of organic nonlinear optics(NLO)by zyss,octupolar molecules have gradually become a research hotspot.The research on the conjugated bridges(π)and the peripheral electron acceptors(A)is relatively mature,while octupolar cores(D)are still limited to benzene,s-triazine,truxene and triindole etc.The more efficient electron-donating octupolar platforms need to be synthesized and studied urgently.Tetraindole(TTI)is a three-dimensional(3D)octupolar conjugated system with S4 symmetry,and triindole(TI)is a planar octupolar conjugated system with C3h symmetry.which have gradually attracted research interest in the field of NLO.The photoelectric properties of conjugated organic molecules are affected by many structural factors,in this thesis,two strategies had been adopted to enhance the NLO effects of the octupolar molecules:(1)introducing the electron-withdrawing groups to improve the intramolecular charge transfer property;(2)extending the π delocalization system by aromatic-fusion manner.In this thesis,the octupolar platforms of the three/two-dimensional charge transfer systems and the π-extended conjugated systems were constructed based on the S4-symmetric octupolar molecule TTI and the C3h-symmetric octupolar molecule TI.1.Three/two-dimensional charge transfer systems:synthesis,structure,NLO effects and hole transport properties.Based on TTI and TI.a series of position-isomerized TTI and TI derivatives(TTI-2-CF3 vs TTI-3-CF3 and TI-2-CF3 vs TI-3-CF3)were synthesized by introducing electronwithdrawing groups(-CF3)at 2-and 3-positions,respectively.The 3D charge transfer systems and planar charge transfer systems were successfully constructed.The crystal structure shows that the shaddle-shaped TTI-2-CF3 maintains the S4 symmetric octupolar structure.The optimized geometries of TI-2-CF3 and TI-3-CF3 possess C3-symmetry with very small dipole moments(0.195 and 0.154 Debye,respectively),indicating that TI-2-CF3 and TI-3-CF3 can be regarded as quasi-octupolar molecules.Among them,TI-2-CF3 crystallizes in the non-centrosymmetric space group Pna21,and the SHG intensity of its powder crystal is one order of magnitude higher than that of KDP(KH2PO4).The absorption and fluorescence spectra presented significantly redshifts.indicating that the charge transfer systems were initially constructed.The redshift of TI-2-CF3 is more significant.The theoretical second-order NLO coefficient βvalue and the theoretical hole mobility μ(1.1 85 cm2V-1 s-1)of TI-2-CF3 are significantly higher than that of its position-isomer TI-3-CF3,indicating that the 2-substitution site is superior to the 3-substitution site in this system.2.π-conjugation extended TTI and TI systems:synthesis,structure,NLO effects and linear photophysical properties.A series of π-extended tetraindole and triindole derivatives(TTIid vs TIid,s-TTIbt vs s-TIbt,a-TTIbt vs a-TIbt,TIph)were synthesized to construct more efficient electron donating octupolar platforms.The crystal structure shows that s-TTIbt maintains S4-symmetric octupolar architecture and crystallizes in P42/n space group.After the aromaticfusion,the absorption and fluorescence spectra showed significant redshifts,indicating that the π-conjugated system was successfully extended.The spectral redshifts of anti-isomers(a-TTIbt and a-TIbt)are larger than that of corresponding syn-isomers(s-TTIbt and s-TIbt).The two-photon absorption(TPA)cross sections(δ values)of the trimers have been measured to be 10-102 times that of the parent TI,and the δ value of the anti-isomer(a-TIbt)has been measured to be 2.7 times that of syn-isomer(s-TIbt)and 102 times that of TI.Compared with the parent TTI and TI,the theoretical NLO coefficients(β values)ofπ-extended TTI and TI derivatives are significantly improved.The theoretical β values of a-TTIbt and a-TIbt are significantly higher than those of s-TTIbt and s-TIbt,and have been calculated to be 2.1 and 4.2 times those of the parent TTI and TI,respectively.Both the experimental spectra and the theoretical calculations demonstrate that the anti-isomer(a-TIbt)formed better conjugated system than the syn-isomer(s-TIbt),which can reasonably explain the more excellent NLO properties of a-TIbt.3.N-phenyl substituted aromatic-fused TI systems:synthesis,structure and photophysical properties.A series of N-phenyl aromatic-fused triindoles(TIid-ph.s-TIbt-ph and a-TIbt-ph)were synthesized by introducing phenyl at the N-H position,which significantly improved the stability of aromatic-fused TI derivatives.These target compounds exhibited excellent fluorescence luminescence properties in solution and solid-state.Due to introducing of the phenyl ring,the absorption and fluorescence spectra displayed significantly redshifts.indicating that the benzene rings at the N atom position also contributed to the conjugation of the whole molecule.The s-TIbt-ph molecules lose the strict planarity,which is caused by the steric hindrance in s-TIbt-ph.The atoms except the N-phenyl group remain basically coplanar.and the phenyl rings on the N atom are biased towards opposite sides of the molecular plane.In summary,we have adopted three strategies to synthesize TTI and TI derivatives to tune the photophysical properties of the target compounds.The crystal structures and solution/solid-state luminescence properties were measured and studied.The nonlinear optical properties(SHG and TPA)were studied theoretically and experimentally.The charge transport properties of partial compounds were studied theoretically.In this thesis,a series of S4-and C3-symmetric octupolar platforms with more excellent NLO responses than parent TTI and TI have been constructed.These compounds can be further acted as efficient NLO octupolar platforms to build more excellent NLO materials and other photoelectric materials by modifying with electron-withdrawing groups in the future.更多还原