Synthesis And Properties Of Triduylboron Environment Sensitive Ratiometric Fluorescent Probes

Viscosity and temperature are important physical parameters.Real-time micro-area viscosity and temperature measurements with high spatial resolution and accuracy can provide important data for understanding the process of changing the state of matter.Traditional viscometers and thermometers are difficult to be used in micro-and nano-scale measurements due to their intrinsic limitations.Non-contact ratiometric fluorescent probes have the advantages of high sensitivity,as well as high accuracy and interference resistance.In this paper,a series of triduylboron compounds have been designed and synthesized,which possess dual intramolecular charge transfer luminescence excited states.The distribution of excited states is affected by viscosity and temperature changes in micro enviroment.The fluorescence of triduylboron compounds has a ratiometric response to temperature and viscosity,and it is an ideal micro viscometer and thermometer.The double emission of triduylboron molecule comes from the ICT excited state and the TICT excited state,and the luminescence properties are affected by affecting the ratio of the ICT excited state and the TICT excited state.Based on this principle,the main content and research progress of this paper are as follows:（1）MPDB1,MPDB2 and TPB1 were synthesized which substituted by4-morpholinepiperidine,pyrrolidine and bromine atoms.The fundamental photophysical properties of this series of compounds were studied by the measurement of the absorption spectrum,emission spectrum,and the calculation system of fluorescence quantum yield.The fluorescence temperature responsiveness of these compounds was studied.In the temperature range from 100°C to-50°C,the luminescence peak wavelength of the MPDB1 compound changed from 483.6 nm to 533.8 nm,and the overall shift was 50.2 nm;the luminescence peak wavelength of the MPDB2 compound changed from 481 nm to 528 nm,and the red-shifted 47 nm;the luminescence peak wavelength of the TPB1 compound changed from507 nm to 558.2 nm,the overall shift is 51.2 nm.The light intensity changed regularly and smoothly with temperature,the emission spectrum gradually shifted to red as the temperature decreased,and the luminescence color also changed from blue to green.Therefore the triduylboron compounds have sensitive temperature responsive fluorescence and can be used as highly accurate molecular fluorescence thermometers.（2）The triduylboron compounds were added to different proportions of glycerol-methanol mixed solutions,and the fluorescence spectra were measured at 20℃and0℃,respectively.Based on this,the fluorescence viscosity responsiveness of these compounds was studied.The viscosity（cp）of the glycerol-methanol mixed solution was calculated with reference to the glycerol ratio and temperature,and the viscosity response range of MPDB1 was 73.7-2463 cp,the viscosity response range of MPDB2 was 17.2-12112cp,and the viscosity response range of TPB1 was 8.03-274 cp,it can be seen that the number of substituents affects the viscosity response range.Overall,with the increase in viscosity,the emission spectrum of such compounds gradually blue shifted,and the emission color changed from green to blue.It can be seen that these compounds have obvious fluorescence viscosity responsiveness,and have the potential to be used as a new type of molecular ratiometric fluorescence viscosity probe.（3）A solid fluorescence thermometer was prepared by dissolving the triduylboron compound in polyethylene glycol 4000.In the temperature range from 60°C to-20°C,the luminescence peak wavelength of MPDB1 changed from 510.6 nm to 470.2 nm,shifted by40.4 nm;the luminescence peak wavelength of MPDB2 changed from 506.2 nm to 466.6 nm,shifted by 39.6 nm;and the luminescence peak wavelength of TPB1 changed from 530 nm to482.6 nm,Moved 43.8 nm.The fluorescence intensity changes regularly and smoothly with temperature,and the emission spectrum gradually blue shifted as the temperature decreases,and the emission color changed from green to blue.It can be seen that the addition of the triduylboron compound to the solid polymer is suitable for use as a solid fluorescence thermometer.For comparison,a series of solid rare-earth complexes were also synthesized in this subject.The solid rare-earth complex uses trifluoroacetylacetone as a ligand,and adds europium（III）chloride hexahydrate,terbium chloride hexahydrate,samarium chloride hexahydrate,and dysprosium chloride hexahydrate.Among them,Eu L₃,Tb L₃,Eu_0.5Tb_0.5L₃and Eu_0.62Tb_0.38L₃have fluorescence temperature responses,but Eu L₃changes irregularly with temperature,while Sm L₃and Dy L₃have no luminescence phenomenon under UV lamp irradiation,so they cannot be used as fluorescence thermometers.The intensities of Tb L₃,Eu_0.5Tb_0.5L₃and Eu_0.62Tb_0.38L₃change regularly with temperature and can be used as intensity-type solid fluorescence thermometers.