Stacking mode modulation of blue light emission from alkaline earth metal organic frameworks
Solvothermal reactions of Ca(NO3)2,Sr(NO3)2 with 2,5-thiophene dicarboxylic(TDC)in N,N'-dimeth-ylformamide(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 analy-sis and IR spectra.Both compounds feature three-dimensional frameworks based on the versatile coordinated modes(μ3-η2∶η2,μ3-η2∶η1,μ2-η2∶η1)of carboxylic groups in TDC ligands.C—H…S hydrogen bonds and C—H… π interactions 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 ligand-to-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 elec-trons rich in the metal centers,thus,generating luminescence through the transition of ligand to metal charge.
alkaline earth metal compound2,5-thiophene dicarboxylicphotoluminescencetheoretical cal-culation
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