【作者】 于杰；

【导师】 李新贵；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2022， 博士

【摘要】 聚集诱导发光（Aggregation-induced emission,AIE）材料指的是一类在溶液中不发光,在晶体、粉末和薄膜等聚集态中显著发光的新型光电材料。根据其发光类型可分为荧光AIE体系和磷光AIE体系。经过多年发展,AIE材料在光电器件、信息传感与生物成像等领域获得广泛认可。目前,AIE分子体系多为通过化学键共轭的有机芳香结构,并通过键连共轭实现了性能优异的可见光和近红外发射。与此同时,由于AIE体系通常具有扭曲的分子构型,芳香基团间可以通过空间进行电子交流,形成空间共轭。然而,复杂的激发态弛豫过程、不同的多重态发光体系和微弱的空间电子交流导致空间共轭效应对AIE材料发光性能影响的研究缺乏系统性。故本文开展空间共轭效应对芳香基有机固体发光材料性能影响的研究,具体研究内容如下:为了研究空间共轭效应对固体荧光材料发光性能的影响,通过铃木反应制备得到两种由四苯基乙烯（TPE）结构单元组成的轴烯大环分子1a和1b,并研究大环分子1a和1b的发光性能。由于TPE基团的存在,1a与1b均表现出显著的AIE性能;但取代基的差异导致二者发光性质存在明显差异。当混合溶剂中水的体积分数增加到60%后,1a的荧光发射发生红移,这与1a聚集体由纤维状晶体变为不规则颗粒直接相关。在不规则颗粒中,1a分子采取更合适的空间共轭分子构型,使能隙降低,荧光发射红移。1b分子由于甲基取代基的影响,具有更好的溶解性和更大的空间位阻效应,不存在聚集体形貌依赖的荧光红移现象。在明确空间共轭效应可以影响固体荧光材料的发光性能后,开展空间共轭效应对有机固体磷光材料性能影响的研究。通过乌尔曼偶联反应和铃木反应制备得到9,9-二甲基氧杂蒽桥连的空间共轭结构材料XP2T、XP2F和XPC。单晶结构分析发现供体与受体面对面紧密排列,间距小至3.20（?）。室温时,在XP2T、XP2F和XPC晶体的发光光谱中,磷光占比高达97%、86%和99%,获得近乎纯磷光发射。通过对比研究发现,XP2T、XP2F和XPC的磷光发射仅源自吩噻嗪基团。结合自旋轨道耦合矩阵元素计算和能级计算,提出空间共轭自旋轨道耦合的新机制:在空间共轭结构中,当供体的S₁与受体的T_n能级接近时,供体和受体间的空间共轭可以促进自旋轨道耦合,提升系间窜跃速率和磷光发射性能。在高效的空间共轭自旋轨道耦合作用下,XPC的系间窜跃速率高达1.2×10⁹ s^-1。在确定空间共轭效应对磷光发射性能的促进作用后,开展空间重原子效应对材料发光性能影响的研究。制备得到氢或卤素原子取代的9,9-二甲基氧杂蒽桥连吩噻嗪衍生物XPH、XPF、XPCl、XPBr和XPI,氢或卤素原子与三线态生成中心吩噻嗪基团通过氧杂蒽基团桥连。在晶体中,重原子效应对材料发光性能有显著的调控作用。在XPBr晶体的稳态光致发光光谱中,磷光占比高达93%,高于XPCl晶体的62%和XPI晶体的75%;XPBr晶体的磷光寿命为5.8 ms,大于XPCl晶体的0.8 ms和XPI晶体的0.1 ms。单晶结构分析发现,空间重原子效应通过空间p-π共轭作用于吩噻嗪基团上。Br的空间重原子效应可以促进吩噻嗪基团的系间窜跃,Br与吩噻嗪基团间的空间p-π共轭可以稳定三线态激子,使XPBr晶体的磷光发射速率与三线态激子非辐射跃迁速率小于XPCl与XPI;I强烈的空间重原子效应使XPI晶体的系间窜跃速率、磷光发射速率与三线态激子非辐射跃迁速率比XPBr高一个数量级。在空间p-π共轭与空间重原子效应的协同作用下,XPBr晶体的量子效率和磷光寿命显著提升。为进一步研究不同距离的空间共轭效应和空间重原子效应对材料发光性能的影响,选取萘作为桥连基团。对比NPH、NPBr和NPI的光致发光光谱与时间分辨衰减曲线发现,更近距离的空间重原子效应可以淬灭吩噻嗪基团的荧光发射,而键连的内部重原子效应会极大地缩短萘基团的磷光寿命。在萘桥连的空间共轭结构中,吩噻嗪基团在生成三线态激子后可以自身发射磷光或将能量传递给萘基团。NP2F中的吩噻嗪基团倾向自身发射短寿命磷光,NP4T中的吩噻嗪基团倾向将大部分三线态能量传递给萘基团,并发射长寿命磷光。此外,NPH@PVA薄膜的余辉长达3.2 s。本文通过研究空间共轭效应对材料发光性能的影响,探索新型聚集诱导发光材料的发光机制,为新型有机固体发光材料的开发和应用提供理论基础。更多还原

【Abstract】 Aggregation-induced emission（AIE）luminescent materials are non-emissive in solution but highly emissive in aggregate state like crystal,powder and film.AIE materials can be divided into two categogries,fluorescent AIE system and phosphorescent AIE system,according to emission type.After over 20 years of development,AIE materials are widely recognized in photoelectronics,information sensing and bioimaging.Currently,the majority of AIE luminogens are aromatic organic molecules conjugated through bonds and the emission can cover visible and near infrared region with prominent properties.Meanwhile,the aromatic groups in AIE molecules can interact with each other through space so that effective through-space conjugation is formed.Though through-space conjugation has effect on the performance of luminescent materials due to the complicated excited state relaxation process,different multiplet emission system and weak through space electron communication,the impact of though-space conjugation on the performance of aromatic luminescent materials lacks of systematic research to study the mechanism.Therefore,the theme of this dissertation is to study the impact of through-space conjugation on the performance of aromtic organic solid-state luminescent materials.The details of this study are as follow:To confirm the influence of through-space conjugation on the performance of organic luminescent materials,two macrocyclic molecules 1a and 1b composed of tetraphenylethylene（TPE）units solely have been prepared through Suzuki reaction to study their photoluminescent properties.Because of the TPE units,both 1a and 1b exhibit excellent AIE properties.However,there’re subtle distinctions between the photoluminescence（PL）spectra of 1a and 1b due to the introduction of methyl in 1b.When the water volume fraction of the mixed solvent is above 60%,the PL peak of 1a red-shifts.The red-shift is the result of morphology of 1a aggregates changing from fibrous crystals to irregular particles.1a molelcules adopt a more through-sapce conjugated conformations in the irregular particles so that the energy gap decreases and the emission red-shifts.Nevertheless,the emission of 1b does not exhibit polymorphism-dependent red-shift due to the better solubility and increased steric hidrance.After confirming the influence of through-space conjugation on the fluorescent properties of organic solid-state materials,the study of the impact of through-space conjugation on the phosphorescent materials is conducted.Through-space conjugated phosphorescent materials XP2T,XP2F and XPC bridged by 9,9-dimethylxanthene have been prepared through Ullmann coupling reaction and Suzuki reaction.According to single crystal XRD analysis,the donor and acceptor are aligned cofacially with a distance short to 3.20（?）.At room temperature,XP2T,XP2F and XPC crystals emits nearly pure phosphorescence with phosphorescence ratio of 97%,86%and 99%,respectively.On the basis of analysis and comparison of PL spectra and decay curves,the phosphorescence solely originates from phenothiazine group.Supplemented with spin-orbital coupling（SOC）matrix calculation and energy level calculation,a concept of through-space conjugation SOC is proposed.When S₁ of donor and T_n of acceptor are degenerate in a through-space conjugated system,the through-space conjugation between the donor and acceptor can facilitate SOC,enhance the rate of intersystem crossing(k _ISC)and phosphorescence-emitting performance.The k _ISC of XPC is up to 1.2×10⁹ s^-1 owing to the highly efficient through-space conjugation SOC.The study of through-space heavy atom is carried out after demonstrating the facilitating effect of through-space conjugation on SOC and phosphorescence-emitting properties of organic materials.Hydrogen or halogen atom substituted phenothiazine derivatives XPH,XPF,XPCl,XPBr and XPI which are bridged by 9,9-dimethylxanthene were prepared to study the influence of through-space heavy-atom effect on the performance of luminescent materials.The substituted atom and the triplet exciton generating center phenothiazine group are bridged by 9,9-dimethylxanthene.Heavy-atom effect has a significant impact on PL properties of the crystal materials.The ratio of phosphorescence in steady-state PL spectra for XPBr crystal is 93%,while the ratio is 62%for XPCl and 75%for XPI.The phosphorescence lifetime of XPBr crystal is 5.8 ms,while the lifetime is 0.8 ms for XPCl and 0.1 ms for XPI.Heavy-atom effect is imposed on phenothiazine group by through-space p-πconjugation according to single crystal analysis.Br atoms in XPBr crystals can facilitate intersystem crossing of phenothiazine group and the through-space p-πconjugation between Br atom and phenothiazine group can stabilize triplet excitons and keep the rate of triplet exciton radiative transition（k _P）and rate of non-radiative transition(k _TS)lower than XPCl and XPI,while the strong through-space heavy-atom effect of I atom makes k _ISC,k _P and k _TS of XPI one order of magnitude higher than XPBr.Therefore,PL quantum yield and phosphorescence lifetime of XPBr crystal increased significantly due to the synergistic effect of through-space p-πconjugation and through-space heavy atom effect.Naphthalene is chosen as bridge group to study the influence of shorter distance through-space conjugation and through-space heavy-atom effect on the perforamce of luminescent materials.It is proved that through-space heavy-atom effect can quench the fluorescence of phenothiazine group in NPBr and NPI while through-bond heavy atom effect reduces the phosphorescence lifetime of naphthalene group by comparing PL spectra and time-resovled decay curves of NPH,NPBr and NPI.As for the naphthalene bridged through-space conjugated structure,triplet excitons of phenothiazine groups can either emit phosphorescence or transfer the energy to naphthalene groups.Phenothiazine groups in NP2F tend to emit phosphorescence by themselves,while phenothiazine groups in NP4T tend to transfer most of its triplet energy to naphthalene groups and emits phosphorescence with long lifetime.Meanwhile,the afterglow of NPH@PVA is up 3.2 s at room temperature.By studying the influence of through-space conjugation effect on the performance of materials,the mechanisms of novel AIE materials were explored,laying a solid foundation for the development and application of solid organic photoluminecent materials.更多还原