基于多酸与1 ,4 ,5 ,8-萘二酰亚胺衍生物的稀土有机-无机杂化材料的设计与合成

基于有机-无机杂化材料的理念，利用稀土硝酸铽[Tb（NO₃）₃]、有机配体BINDI (BINDI=N,N′-双（5-间苯二甲酸）-1,4,5,8-萘二酰亚胺)及Keggin型多酸H₄SiW₁₂O₄₀·26H₂O在溶剂热的条件下反应，成功合成出多酸基稀土配位聚合物Tb₄[SiW₁₂O₄₀]·[BINDI)]₂·[DMA]₁₆。采用X-射线单晶衍射仪、X-射线粉末衍射仪、红外光谱仪、热重分析仪、紫外-可见吸收光谱仪、元素分析仪、荧光光谱仪和电子顺磁共振仪对稀土聚合物的结构组成、热稳定性、发光性能以及光致变色性能进行了表征。X-射线单晶衍射分析发现该稀土配位聚合物结晶于Tetragonal晶系，空间群为P4₂/n，展现出3D手性双螺旋网络结构特征，其中多酸阴离子SiW₁₂O₄₀(简写为{SiW₁₂})镶嵌在稀土有机基团形成的孔道中；红外及紫外吸收光谱分析发现稀土Tb3+与配体（BINDI）配位成键；荧光光谱表明，在380 nm的激发波长下，配体显示出最强荧光发射峰，位于441 nm处，而化合物的最强发射峰位于471 nm处。由于三价铽离子不易被氧化也很难被还原，所以化合物的荧光发射不能归因于金属与配体之间的电子辐射跃迁，且化合物的发射峰与配体的发射峰比较相近，因此荧光主要是配体BINDI的发光。另外Tb(Ⅲ)离子的特殊跃迁发射带没有出现是因为在荧光测试时由于光照的原因导致样品的颜色发生了突变，即发生了光致变色的现象，导致光诱导电子转移以致荧光猝灭。引起金属配合物荧光猝灭的原因通常是光致电子转移，而电子转移的方向是配体中的电子向金属空轨道转移（LMCT）所致，形成配合物后其最大发射峰红移或蓝移是由电子转移导致分子内电子分布的改变，从而引起HOMO-LUMO能隙的减小或增大所致，与配体荧光光谱相比，化合物的发射峰发生了红移。此外，电子顺磁共振结果表明由于化合物中的BINDI配体在紫外与可见光照射下发生电子转移形成配体自由基，以及多酸在光激发下，发生W5+→W6+的过程进一步促进该化合物发生光致变色现象。因此，该化合物具有极其敏锐光致变色的性质。

Design and Synthesis of Rare Earth Organic-Inorganic Hybrid Material Based on Polyoxometalate and 1,4,5,8-Naphthalenediimide Derivatives

Based on the concept of organic-inorganic hybrid materials, take advantage of the fact that rare earth terbium nitrate [Tb(NO₃)₃], organic ligands BINDI (BINDI=N,N′-bis (5-isophthalic acid)-1,4,5,8-naphthalenediimide and the Keggin-type polyoxometallate H₄SiW₁₂O₄₀·26H₂O will react under solvothermal conditions to successfully synthesize a polyacid rare earth coordination polymer Tb₄[SiW₁₂O₄₀]·[BINDI)]₂·[DMA]₁₆. The structure, composition, thermal stability, luminescence properties and photochromic properties of the rare earth polymer are characterized by X-ray single crystal diffractometer, X-ray powder diffractometer, infrared spectrometer, thermal gravimetric analyzer, ultraviolet-visible absorption spectrometer, elemental analyzer, fluorescence spectrometer and electron paramagnetic resonance spectrometer. X-ray single crystal diffraction analysis revealed that the rare-earth coordination polymer is crystallized in the tetragonal crystal system, and the space group is P4₂/n, exhibiting the 3D chiral double helix network structural characteristics. Among them, the polyacid anion SiW₁₂O₄₀ (abbreviated as {SiW₁₂}) is embedded in the pores formed by rare earth organic groups; Through infrared and ultraviolet absorption spectroscopy analysis we found that rare earth Tb3+ and ligand (BINDI) have been coordinated to form a bond; Fluorescence spectroscopy indicated that at the excitation wavelength of 380 nm, the ligand shows the strongest fluorescence emission peak at 441 nm, while the strongest emission peak of the compound is at 471 nm. Since the trivalent europium ion is not easily oxidized and is difficult to be reduced, the fluorescence emission of the compound cannot be attributed to the electron radiation transition between the metal and the ligand, and the emission peak of the compound is similar with the emission peak of the ligand. Therefore, the fluorescence is mainly the luminescence of the ligand BINDI. In addition, the special transitional emission band of Tb(Ⅲ) ions does not appear, because the color of the sample has break due to illumination during the fluorescence test, that is, the phenomenon of photochromism has arisen, resulting in photoinduced electron transfer to cause fluorescence quenching. The reason for the fluorescence quenching of metal complexes is usually photoelectron transfer, and the direction of electron transfer is the transfer of electrons in the ligand to the metal orbit (LMCT). The red shift or blue shift of the maximum emission peak after complex formation is caused by the change of electron distribution in the molecule resulting from electron transfer, which gives rise to the decrease or increase of the HOMO-LUMO energy gap. The fluorescence spectrum of the compound is red-shifted compared to the fluorescence spectrum of the ligand. Furthermore, electron paramagnetic resonance spectrometer manifests that owing to the electron transfer of the BINDI ligands in the compound to form free radicals under ultraviolet and visible light irradiation, and the polyoxometallate under light excitation, the occurrence of W5+→W6+ further promotes the photochromism of the compound. Therefore, the compound has extremely acute photochromic properties.