新颖钟摆型分子基铁电化合物的可控构建

Compared with traditional inorganic ceramic ferroelectrics, molecular ferroelectrics have the special advantages, and become a kind of functional materials with wide applications. However, the present study of molecular ferroelectric is still in the semi-empirical stage, most of the obtained molecular ferroelectrics are screened out by lots of preparations. Therefore, it is an urgent task to rational design and synthesis new molecular ferroelectric. Inspiration by the stator-rotor ferroelectric model, in this project, we propose a pendulum model for molecular ferroelectric, that is a metal complex [R-(NNN)MX3] (R= organic chains, M = metal, X = halogen) with a long chain of chelating ligand. Due to the organic long chain is easy to have thermal motion and acts as a swing, the three teeth chelate is a stator because of its strong rigidity and large group, which realization of intramolecular dipole structure. When the model compound is from high temperature to low temperature, the crystal will have a disordered to ordered phase transition. The mains researches contained: the design and synthesis the long tail ligands and their metal complexes; characterization of ferroelectric properties of model compounds; The influence of the size of the long chain group and the type of metal halide on the ferroelectric properties will be studied; the microscopic mechanism for the generation of phase transitions and ferroelectric properties will be addressed. Therefore, this project has important theoretical significance and practical application prospect in the exploration of new type of phase transition ferroelectric materials.

与传统无机陶瓷铁电相比，分子基铁电体表现出特殊的优势成为一类具有广泛应用前景的功能材料。由于目前对分子铁电的研究仍处于半经验阶段，多数分子铁电体都是通过大量合成筛选得到，因此有意识的设计合成新型分子基铁电成为一项紧迫的任务。受定子-转子铁电模型的启发，本申请我们将设计合成新型钟摆分子基铁电化合物[R-(NNN)MX3] (R = 有机长链，M = 金属，X = 卤素)。利用有机长链易于做热运动而成为摆子，三齿螯合物由于刚性强，基团大而成为定子，实现分子内的双偶极结构。当此模型化合物从高温到低温时，晶体将发生无序到有序的相变，从而可能获得新型分子基铁电体。具体研究包括：长链三齿配合物的设计合成；模型化合物铁电性能的测试表征；研究长链基团和金属卤化物对铁电性能的影响，揭示相变和铁电性能产生的微观原因。因此本申请对有目的的设计合成新型分子基相变铁电体材料具有重要的理论和实际应用价值。

据我们所知，具有结构相变的主-客体冠醚包裹体在外部温度刺激下很容易改变空间结构，因为它们的原子位置可以从一个平衡移到另一个平衡。这一变化过程有利于诱导SHG活性。近年来，我们专注于高质量的二阶非线性光开关材料的设计。然而，将抽象的动量匹配原理转化为具体的化学方法来设计具有高相变温度和可切换SHG活性的主-客体冠醚包体仍然是一个挑战。本文通过2,6-二氟苯胺(DFBA)与1,4,10,13-五氧杂环十五烷(15-crown-5)在HClO4或HReO4水溶液中反应，成功设计并制备了两种新型主-客体冠醚超分子[(DFBA)(15-crown-5)]X (X = ClO4−，1;ReO4−，2)。引入二氟取代苄基酰胺作为客体阳离子后，1和2的相变温度分别提高到377 K和391 K。更重要的是，当高氯酸盐(ClO4−)被更大、更重的每酸盐(ReO4−)取代时，1的空间群从中心对称(CS) P2/c转变为非中心对称(NCS) Pca21，导致2表现出可切换且稳定的二次谐波产生(SHG)效应。根据正离子和阴离子动量匹配的原理，高聚物基团增加了分子热运动的能量势垒，这不仅显著提高了2的相变温度，而且使其在室温下被冻结结晶在NCS空间群中。本研究表明，极性分子可以通过实际的化学手段调节晶体内阴离子和阳离子的适宜性。