Tri-emitting MOF-guest Composites:Fabrication And Applications For Chemical Sensing

The“host-guest”composite materials,which are composed of metal-organic frameworks（MOFs）（host）and luminescent modules（guest）,show significant application value in catalysis,drug delivery/imaging and chemical sensing,et al.The dual-emission MOF-guest composites have been widely used in chemical sensing,such as the detection of volatile organic compounds（VOCs）or nitroaromatic compounds（NACs）.The ratio sensing method based on the ratio of the intensity of dual-emission composites has higher accuracy than that of the single emission materials.However,the ability of these sensing materials to distinguish analytes need to be further improved.In addition,these studies mainly focus on the improvement of the properties of the composites,and pay little attention to the influence of guest or environmental factors on the crystallographic diffraction or structure of the host.In-depth understanding of the internal relationship of structure can promote the synthesis of excellent materials.The purpose of this dissertation is to synthesize multiluminescent MOF-guest composites with excellent sensing performance.The influence of guest and environment factors on the host were explored,and combined with theoretical calculation and simulation,the excellent sensing performance of multi-luminescence MOF-based composites were synthesized.Here,a new MOF（1,（Me₂NH₂）[Zn₂（L¹）（H₂O）]·3DMA·3H₂O）with a mesoporous cavity was synthesized.The effects of temperature,guest solvent,crystal size and luminescent module on the single crystal X-ray diffraction and microstructure of the compound were investigated.The results showed that:1)The single crystal diffraction quality of 1,including the average diffraction intensity and the number of diffraction dots at high angles,increased with the increase of temperature（150 to 291 K）.2)The framework of 1 has a reversible anisotropic thermal expansion property.3)Theoretical calculation shows that,with the expansion of the framework,its configuration becomes more stable in thermodynamics,and the structural vibration decreases continuously,thus promoting the diffraction quality of the single crystal.4)The smaller the crystal size of 1,the larger the cavity along the c-axis presents.This phenomenon may be due to the relatively high surface tension corresponding to small size crystals,resulting in larger pressure in the pores to balance the surface shrinkage of particles,thus resulting in larger pore size of crystals with smaller particle size.5)The cavity size of the compound is positively dependent on the size or concentration of the encapsulated luminescent modules（ELMs）.Exploring the influence of environmental factors,crystal size and various luminescent modules on the host of compounds can facilitate our understanding of the dependence of the material microstructure on the influencing factors.Sixteen dual-emission composites including 8 blue-green（[Ir]⁺@1）and 8 blue-red([Ru（bpy）₃]²⁺@1)emission composites,and 7 tri-emissive composites([Ir]⁺+[Ru（bpy）₃]²⁺)@1)were facilely obtained from the respective/simultaneous incorporation of green-and red-emitting complex cations,namely[Ir（CF₃-ppy-F₂）₂（bpy）]⁺and[Ru（bpy）₃]²⁺,into the compound1 by impregnation strategy.The structure and luminescence properties of the composite were characterized.And a white-light-emitting（WLE）composite W2((0.28 wt%[Ir]⁺+0.45wt%[Ru（bpy）₃]²⁺)@1 was presented,CIE coordinates is（0.33,0.34）).W2 recognized DMA or fluorobenzene in a real-time luminescence discoloration.A two-dimensional ratiometric sensing（2-DRS）method further accurately distinguish series of VOCs.When the time as the z-axis of the 2-DRS,a three-dimensional ratiometric sensing（3-DRS）method with higher accuracy is constructed.W2 accurately distinguished nitrobenzene（NB）,o-dinitrobenzene（o-DNB）and m-dinitrobenzene（m-DNB）vapor at 60℃through the 3-DRS;remarkably,W2figured out m-DNB vapor in 30 s based on dramatic changes of the luminescent colour.The detection mechanism is discussed.The recognition methods（2-DRS and 3-DRS）have been proposed to compensate for the inaccuracy of traditional absolute luminescence intensity method and the low sensitivity of single ratio luminescence sensing method.The simulation results show that W2 could only distinguish NACs vapor at least 60℃because[Ir]⁺-ELM and[Ru（bpy）₃]²⁺-ELM blocked matrix holes.Theoretical simulation predicts that the matrix encapsulated acridine module[ACF]⁺with a smaller size probably has a stronger ability to detect/distinguish NACs vapors.Thus,based on the MOF(2,（Me₂NH₂）₃Cd_0.5[Cd₃（L²）₂]·6DMF·9H₂O),a series of dual-/tri-emissive composites were synthesized by a template method.The structural composition and light-emitting properties were characterized in detail.The tri-chromatic composite V4(0.087 wt%[ACF]⁺+0.850wt%[Ru（bpy）₃]²⁺)@2)identified multiple groups of NAC isomer vapors at room temperature.The ability of V4 to detect/distinguish NACs vapors was significantly better than that of W2,which was consistent with the prediction of theoretical simulation.To further quantify the ability of 3-DRS to distinguish analytes,we propose a vector index r,which defines the size and direction of each NAC trajectory in 3-DRS.According to the r relationship of each NAC,the control experiment and theoretical calculation,it was found that the size synergistic effect between ELM and matrix holes,the saturated vapor pressure of NACs,and the non-covalent interactions（NCI）between the composites and NACs were the three main factors affecting the detection and discrimination of NACs.Based on density functional theory（DFT）,the possible electron transfer paths for detecting NACs are discussed.