【作者】 尹升燕；

【导师】 吴立新；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2009， 博士

【摘要】 多金属氧簇是一种单分散的、结构均一的多阴离子簇合物。它具有丰富的拓扑结构、多样的化学组成和独特的物理化学性质,在催化、医药和材料等领域展现了广泛的应用价值。发展合适的方法将多金属氧簇组装到软材料体系中,是扩展其功能应用的有效途径。超分子液晶通过分子识别和自组装,对分子间相互作用加以利用和操控,促进了在更广泛的空间创造新的液晶材料,特别是对探索具有光、电、磁等功能特性的液晶材料的分子设计、合成和应用具有重要意义。将功能性的多金属氧簇通过超分子相互作用引入液晶体系中不但可以制备新颖的有机/无机杂化液晶材料,而且为开发新的多功能液晶材料提供了新的思路。本论文基于静电复合原理,使用阳离子表面活性剂对多金属氧簇进行包覆,形成有机/无机杂化超分子复合物。进而以复合物作为研究对像,系统的考察了多金属氧簇的性质与超分子复合物相行为之间的关系,主要包括以下三方面工作:(1)我们选用了含有质子敏感的偶氮苯基团的表面活性剂,与强酸性Keggin型结构的多金属氧簇静电复合,制备了稳定的质子化液晶复合物。研究发现多金属氧簇的酸性对复合物的液晶性质具有调节作用,这为设计化学刺激响应的液晶材料具有重要意义;(2)我们利用末端带有苯甲酸基团的表面活性剂与Keggin型结构的多金属氧簇静电复合,制备了氢键给体复合物,并将该复合物与含吡啶基团的氢键受体衍生物相结合,构筑了多组分、多作用形式的杂化液晶组装体。研究了含吡啶基团氢键受体尾链的长度和烷基链个数,受体刚性基团的种类以及不同多金属氧簇对组装体液晶性质的影响。这种方法为制备具有功能特性的无机粒子杂化液晶材料,以及调控其液晶相态提供了一种新的策略;(3)我们利用末端带有苯甲酸基团的表面活性剂与荧光型多金属氧簇静电复合,制备了荧光型复合物。苯甲酸氢键二聚体这种无荧光的介晶基团诱导复合物展现出氢键、静电交替的网络结构,并在加热过程中形成了层状液晶相。研究发现通过调节复合物液晶相可以调控复合物的光物理性质,而且在液晶结构中复合物中Eu3+处于一个更加不对称的环境,从而使我们获得了更加纯的红光发射材料;同时在液晶结构中复合物的荧光量子产率有所提高。这些研究为发展荧光型的液晶材料提供了新途径。更多还原

【Abstract】 Polyoxometalates （PMs） are a kind of monodisperse and uniform molecular clusters of the early transition metal oxides, especially for the elements of vanadium, molybdenum and tungsten. The variety of their composition and structures endowed them with many functional properties, such as catalysis, proton conductivity, nonlinear optics, medicine, proton acidity, photophysics and magnetism. However, the development of materials and devices based on PMs was restricted because of their high lattice energies, low pH stability and poor processibility, and great efforts have tried to improve the functionality performance of PMs with the assistance of other matrices. Organic liquid crystal （LC） system is considered as the suitable candidate for combination, location and orientation the clusters, representing the physical and chemical properties of the PMs, due to its organizable properties and good processibility. In this thesis, we have prepared organic/inorganic hybrid supramolecular liquid crystal material, through the supramolecular interaction on multi-component and multi-forms, based on the surfactant encapsulated polyoxometalate complexes （SEP）. In the hybrid materials, the synergy of polyoxometalates and organic liquid crystal molecules realized the mutual adjustment of the intrinsic properties of polyoxometalates and the liquid crystal structures of the complexes.Firstly, we encapsulated Keggin-type heteropolyanions, H₃PW₁₂O₄₀ （HPW）, Na₃PW₁₂O₄₀ （NaPW）, H₄SiW₁₂O₄₀ （HSiW） and K₄SiW₁₂O₄₀ （KSiW）, by a kind of azobenzene-containing surfactant, through the replacement of counterions. The resulting surfactant-encapsulated PM complexes were characterized in detail by UV-vis, Raman, NMR spectra and elemental analysis. The measurement results indicate that some azobenzene groups in the complex L/HPW, L/NaPW and L/HSiW were protonated during the encapsulation due to polyoxometalates’intrinsic strong acidity. In the protonated complex, the ammonium head group of the surfactant and polyoxometalate combine through the electrostatic interaction, and the bromonium ion derived from ion replacement binds to the protonated azobenzene group as a counterion. The thermotropic liquid crystal properties of these complexes were investigated by differential scanning calorimetry, polarized optical microscopy and variable-temperature X-ray diffraction. The protonated complex HL/HSiW reveals SmA and SmC phases, while the corresponding non-protonated complex L/KSiW exhibits only SmB phase. The protonated complexes HL/HPW and HL/NaPW self-organize into SmB phase, similar to that of non-protonated L/HPW. The competitive balance between the phase separation and the volume minimization of surfactants is supposed to play an important role and could be employed to explain the self-organized LC structures of these protonated and non-protonated complexes. Both the number of surfactants on the surface of PMs and the protonation to the azobenzene groups can make the LC phases of SEPs become diversiform, which may exhibit potential applications in developing chemistry stimulation-response hybrid LC materials.Following, we constructed multi-component hybrid LC materials through both intermolecular hydrogen bonding and ionic interaction. In order to achieve this motivation, we designed and synthesized a surfactant with a benzoic acid group at one tail end, and encapsulated the Keggin-type heteropolyanions using this surfactant, obtaining the supramolecular complex which could be served as the donor of the hydrogen bonding. If there is not a mesogen in the hybrids, they will not exhibit LC properties during heating and cooling cycles. So, we chose four pyridine derivatives containing conjugated groups, and have then prepared the hybrids through intermolecular hydrogen bonding between the supermolecular complex and pyridine derivatives. The results imply that the isotropic phase transition temperature of the hybrids increase with increasing alky chain length, number of the pyridine derivatives. And the introduction of stilbene unit to the pyridine derivatives also benefits for the higher isotropic phase transition temperature. We also study the effect of the charge number of polyoxometalate. The organic/inorganic hybrid liquid crystals constructed by multi-forms supramolecular interaction is convenient for us to adjust the liquid crystal phases, through the introduction of the different organic and inorganic components into the liquid crystal system.As the benzoic acid dimer is not a real conjugated group, it should not quench the luminescence of the inorganic PM core while it directs the formation of liquid crystal phases. Based on this point, we encapsulated three Eu-containing PMs with the surfactant containing benzoic acid group, and obtained a serious of surfactant-encapsulated PM complexes with intrinsic luminescence. The carboxyls bearing in the complexes were confirmed existing in the dimer state through intermolecular hydrogen bonding, which leads to stable and reversible thermotropic liquid crystal properties of these complexes. These complexes displayed intrinsic luminescence both in the amorphous powder states and in their mesophases. The photophysical properties showed the dependence on the existing states of samples, and the quantum yields of the complexes in the liquid crystal structures are higher than the corresponding amorphous powders. Specifically, Eu3+ in the complexes shows higher asymmetry in the liquid crystal structure due to its anisotropy than the corresponding amorphous powder, and thus, we have obtained the complexes with more pure red emission in their liquid crystal phases. The present investigation provides an example for developing hydrogen-bonding-induced polyoxometalate-containing hybrid liquid crystal materials with intrinsic luminescence.In summary, we have fabricated functional supramolecular LCs, by using the liquid crystal surfactants to drive and link PMs into the organic LC system. The intrinsic properties of polyoxometalates are well retained in the hybrid liquid crystals, and show an important effect on the liquid crystal phases. And, the liquid crystal phases could also adjust the property of polyoxometalates.更多还原