Fluorescence Modulation And White Light Emission Of Metal-organic Framework Materials

Metal-organic framework materials,also called MOFs,which have good thermal stability and can be controlled,modified and combine with the characteristics of organic and inorganic compounds,becomes a potential fluorescent material.The hybridization of MOFs can provide various possibilities for fluorescent properties.In addition to the luminance of metal centers and organic ligands themselves,multiple options for excitation and emissioin can be performed via energy-transfer from ligand to metal and the luminescent guests that are trapped in the cavities of MOFs,thereby providing opportunities for the fluorescence modulation and white light emission of metal-organic framework materials.MOFs are constructed from metal-containing nodes and organic linkers.Aromatic carboxylic acid ligands can be used as a main connector of MOFs due to their various coordination modes and structural effects caused by weak interactions and hydrogen bonding,and as blue light source and the sensitizers of metal ions which can enhance fluorescence properties.Furthermore,because of their sharp and intense fluorescence emissions,Ln3+ ions with different emission colors can be used to build MOFs whose fluorescence colors can be modulated or white light emission MOF materials.In this work,we have synthesized a series of MOFs using aromatic carboxylic ligands and metal ions.Tunable color and white light emission were obtained by encapsulating different Ln3+ ions in the pores of the MOFs or through a cation-exchange process.The main results are summarized as follows:(1)Three isostructural microporous Ln-MOFs,[H3O][HN(CH3)3]2[Ln3(1,3-BDC)6]3-(1:Ln = Gd;2:Ln = Eu;3:Ln = Tb)with trimethylammonium cations and protonated water molecules residing in their 1D channels have been synthesized via solvothermal reactions.By introducing different amounts of Eu3+ and Tb3+ions into the blue emission Gd framework,a series of color tunable and white light emission materials were obtained.In addition,the compound 2 was selected to explore the sensing behavior for metal ions.It displays a sensing ability to Co2+,Cu2+,Mn2+ and Ni2+ ions and selective sensing ability to Fe2+ and Fe3+ ions.(2)A highly connected(5,5,18)-c trinodal net,[Cd2K4(2,3-PDC)4](4)(2,3-H2PDC =2,3-pyridinedicarboxylic acid)has been synthesized by a solvethermal method.The structure of 4 features a 3D heterometallic inorganic connectivity with a diamond topology.Luminescent study shows that the emission of 4 can be tuned from green to blue via variation of the excitation wavelength and a white-light emission is readily realized by encapsulating a certain amount of Eu3+ ions into the framework of 4.(3)Four Ln-MOFs,[H2N(CH3)2]4-[Eu2(OH-BDC)5](5),[Eu2(Me-BDC)3]·(CH3CH2OH)(6),[Eu2(BPT)2(CH3CH2OH)(H2O)3]·(H2O)2(7)and[Eu2(m-BDC)3(phen)2](H2o)(8)were synthesized from the reactions of different aromatic carboxylic acids with Eu3+ions.The structures and thermal stability of these compounds were analyzed by single-crystal X-ray diffraction,XRD,TGA and IR.Their fluorescence properties wer also investigated.