| In recent years, photosensitive MOFs embedded with photosensitive units in the pore wall or channels as an innovatory subclass of MOF with high surface areas, tunable porosity, photosensitive nature are now receiving extensive attentions, due to not only their unique esthetics, but also their broad applications in many fields such as gas storage/separation, luminescence, magnet, catalysis, sensor, battery, and so on. In this work, according to the current social needs and the fundament of the crystal engineering, three types of Ln-MOFs were successfully synthesized by selecting 11 kinds of lanthanide metal nitrate and chlorate（Lanthanide metal includes: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er） to build metal centers and chose Azobenzene-4,4’-dicarboxylic acid（H2AzDC） as oxgen ligand with solvo/hydrothermal method. The synthesis is realized by regulating or changing the type and volume of DMF and DMSO. Furthermore, the structure, thermo and solvent-stability, characteristics of hole wall,photosalient effect and gas adsorption of the three series of Ln-MOFs were contrastively studied. The details were summarized under three parts:（1） Nine MOFs were successfully synthesized by selecting 9 kinds of lanthanide metal nitrate（Lanthanide metal includes: Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er） to build metal centers, the reaction solvent was DMF. The nine crystal was identified as the same phase by single crystal X-ray structure characterization and powder diffraction analysis, namely Ln-1-MOF. In this work, we chose Ln-1-1（Gd） as an example of Ln-1-MOF to study. The analysis of hole wall and ultraviolet light research show that along the c axis, the structure reveals a flexible rhombus hole, where the photosensitive –N=N– units are highly dense and ordered and show almost identical orientation and linear alignment; We investigated the photomechanical motion of the single crystal of Ln-1-1（Gd） in mother liquor under UV irradiation, showing the material has a very good light sensitivity; In addition, we explored the photoresponsive effect of crystal in ethanol under/without UVirradiation through Uv-vis spectrophotometer; Furthermore, pore structure was characterized by nitrogen adsorption at 77 K, the adsorption isotherms of CO2, CH4, CO, O2 and N2 gases were measured at 293 K, respectively; Moreover, p-xylene adsorption property has been characterized.（2） Two MOFs were synthesized by selecting La（NO3）3·7H2O and Ce（NO3）3·6H2O as metal salts and choosing DMF as reaction solvent. The two crystals were identified as the same phase by single crystal X-ray structure characterization and powder diffraction analysis, namely Ln-2-MOF. In this work, we chose Ln-2-1（La） as an example of Ln-2-MOF to study. The analysis of hole wall and ultraviolet light research show that along c direction, the exceptional nine-coordination of La（III） ions induces the insertion of additional AzDC2- connectors in the rhombus hole. The ultraviolet light research shows that the photoresponsive time delay and the effect is weakened. In addition, subsequent studies have shown that the control of axial ligands of AzDC2- and big angle between azo molecule configuration is the reason of light response effect being weakened. Moreover, we tested the adsorption property and adsorption selectivity of Ln-2-1（La） for CO2, CH4, CO, N2, O2 at 295, 273 K, respectively. Pore volume and BET surface area were confirmed by nitrogen adsorption at 77 K.（3） Immerging the eleven crystals of nine Ln-1-MOFs and two Ln-2-MOFs in DMSO about 2 days, we found that the eleven crystals being soaked were identified as the same phase by single crystal X-ray structure characterization and powder diffraction analysis, namely Ln-3-MOF. The wall analysis reveals that both “single-walled†and “double-walled†arrays of AzoDC2- ligands in Ln-3-MOF are observed; the “single-walled†fashion shows a very loose array and the “double-walled†fashion shows the highly irregular. we predicted that the photosalient effect in Ln-3-MOF was turned off and finally the prediction was confirmed through ultraviolet light research; In addition, we also studied the stability of Ln-1-1（Gd） in CH3 OH, CH3CH2 OH, DMF, DMSO, and so on and found the Ln-1-1（Gd） only could survive in DMF and DMSO; The investigations disclosed that photosalient effect in Gd-Azo MOF is highly sensitive to solvents and facilitates to read out DMF or DMSO by naked eyes through turn-on/off photosalient effect. |
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