Construction Of Host-Guest Metal-Organic Frameworks With Dual-Emitting And Their Fluorescence Temperature Sensing

Temperature is a basic physical parameter,the rapid and precise measurement of it is of great significance in many fields,including scientific research,industrial production and daily life.The non-contact optical temperature sensing strategy has attracted extensive research interest due to its advantages,including fast response,accuracy,and capability of working under extreme environmental conditions such as high voltage and strong electromagnetic fields.The ratiometric temperature sensor based on dual luminescent intensity ratio can endow the system with self-calibrated ability,thus showing a broad application prospect.Luminescent metal-organic frameworks(LMOFs)combine the designability of MOFs and abundant luminescence sites simultaneously,making them excellent candidate materials for fluorescence thermometers.At present,most of the fluorescent MOFs thermometers focus on the ratiometric temperature sensing of dual metals MOFs(Eu Tb MOFs),but the further development of the properties and material system is limited because of the fixed emission wavelength and the scarcity of rare earth elements.The designability of fluorescent MOFs of host-guest system is much higher than that of Eu Tb system,which has attracted wide attention in recent years.MOFs with specific channels or functional sites can be employed to accommodate or embed a wide variety of luminescent guests.Through reasonable design,electron/energy transfer can occur between hosts and guests,and then affect their luminescent behavior.In this dissertation,different types of host frameworks and a variety of luminescence guest species are selected to construct a series of host-guest fluorescence temperature sensors.Two types of isostructal MOFs,ZJU-56 and Zn PZDDI,with one-dimensional pores were constructed by solvothermal method adopting 5,5?-(pyrazine-2,5-diyl)diisophthalic acid(H4PZDDI)and 5,5?-(pyridine-2,5-diyl)diisophthalic acid(H4PDDI)with exposed N sites as organic ligands.Two luminescent guest species,organic dye DSM and rare earth ion Eu³⁺,are embedded into the host frameworks by means of ion exchange and covalent binding.DSM@ZJU-56 and DSM@Zn PZDDI,Eu³⁺@ZJU-56 and Eu³⁺@Zn PZDDI were obtained,and all the hybrids showed dual emission from the linkers and the guests.The temperature sensing performance of the DSM-incorporated system and the Eu³⁺-incorporated system in the physiological range(298-358 K)and the physiological-high temperature range(298-478K)were investigated respectively.Temperature dependence of luminescence spectra and the the fluorescence lifetime confirms the different effective energy interaction between the host frameworks and the guests,which provides a guideline for designing novel host-guest composites with fast response and high sensitivities over a broad temperature range.ZIF-8 was employed as the host framework,carbon quantum dots(CQDs)and rhodamine B(RB)as luminescence guest species.Single-phase single-shell CQDs/RB@ZIF-8²and single-phase multishell CQDs@ZIF-8²@RB@ZIF-8²nanocomposites were prepared by solvent-mediated layer-by-layer growth,respectively.In addition,the mixed matrix membranes were prepared by mixing the obtained nanocomposites into poly(vinylidene fluoride)(PVDF).The ratiometric temperature sensing based on dual emission of CQDs and RB of two film hybrids in the physiological temperature range(20-80 ^oC)were realized.The accurate spatial arrangement endows the materials with different energy transfer processes,thus achieving different performance.PCN-700 was selected as the matrix,because its coordinatively unsaturated Zr6 clusters and bcu network provide two types of pockets for the guest molecules.Based on this,linear organic ligands,4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dibenzoic acid(H₂BTDB)with high quantum efficiency and[2,2'-bipyridine]-5,5'-dicarboxylic acid(H₂BPYDC)with excellent auxiliary luminescence properties,with different lengths were imbedded in the matrix and the exposed Lewis alkaline N sites on BPYDC were further used to covalency Eu³⁺to obtain PCN-700-BTDB-BPYDC@Eu³⁺.The multiple internal energy transfer process makes the hybrid the characteristic emission of both the BTDB and Eu³⁺.The changes of luminescence behavior were studied in the physiological-high temperature range,and the high sensitivity and obvious color changes confirmed the potential application ability of the materials.Moreover,the effects of different assembly sequence on the synthesis and properties of the hybrids were investigated.This work provides a new approach for the development of multi-component and dual-emitting hybrid materials.