碱土金属有机框架蓝光发射的堆积模式调制

Stacking mode modulation of blue light emission from alkaline earth metal organic frameworks

Ca(NO_(3))_(2),Sr(NO_(3))_(2)和2,5-噻吩二羧酸(TDC)在N,N‘-二甲基甲酰胺(DMF)的溶剂热条件下合成了两种有机-无机杂化框架化合物[M(TDC)(DMF)]n(M=Ca(1),Sr(2)),对其进行X射线单晶衍射、X射线粉末衍射、元素分析、红外光谱表征.两个三维骨架化合物中的TDC配体的羧酸表现灵活多变的连接方式(μ^(3)-η^(2):η^(2),μ^(3)-η^(2):η^(1),μ2-η^(2):η^(1)),化合物中C-H···S的氢键和C-H···π作用使化合物结构更稳定.观察到两个化合物发出蓝光和蓝绿色荧光,相比于它们异构体的配体中心的荧光,它们的发光机理归属为配体到金属间的电荷转移(LMCT),而不是同分异构体中配体中心的发光.电子结构计算表明,在较弱的堆积力作用下,可以获得较大的间隙,有利于LMCT的发生.这一结果表明,硫杂原子的引入会导致更多电子富集在金属中心附近,从而产生从配体到金属电荷跃迁方式的发光.

Solvothermal reactions of Ca(NO_(3))_(2),Sr(NO_(3))_(2) with 2,5-thiophene dicarboxylic(TDC)in N,N΄-dimethylformamide(DMF)afford two new inorganic-organic hybrid frameworks,[M(TDC)(DMF)]n(M=Ca(1),Sr(2)),which have been characterized by single-crystal X-ray diffraction,powder X-ray diffraction,elemental analysis and IR spectra.Both compounds feature three-dimensional frameworks based on the versatile coordinated modes(μ^(3)-η^(2):η^(2),μ^(3)-η^(2):η^(1),μ2-η^(2):η^(1))of carboxylic groups in TDC ligands.C-H···S hydrogen bonds and C-H···πinteractions contribute to the stabilization of the structures.Consequently,blue and blue/green luminescence of two compounds has been observed.Their luminescence mechanism can be ascribed to ligandto-metal charge transfer(LMCT)compared with the ligand-centered luminescence in their isomers.Electronic structural calculations illustrate that under the condition of weaker packing forces,larger gaps can be achieved,which facilitate the LMCT.The result suggests that the introduction of S-heteroatom can result in more electrons rich in the metal centers,thus,generating luminescence through the transition of ligand to metal charge.