Fluorescence Characteristics And Adjustment Of Organic Pyridine Salt DAST

Fluorescence is the light emitted by a substance after absorbing light or other electromagnetic radiation.It has been widely applied in the fields of medicine,biology,agriculture,industry,and environmental science.Compared with inorganic fluorescent materials,organic materials have diverse structures and good tunability.Among them,organic pyridine salts have attracted considerable attention.4-N,N-Dimethylamino-4′-N′-methyl-stilbazolium tosylate（DAST）,as an important organic pyridine salt,not only exhibits excellent nonlinear optical properties,but also has obvious fluorescence.However,results about its fluorescence are not systematic and in-depth to date.So,the photoluminescence properties of DAST-based materials and the fluorescence regulation were investigated in this thesis.The main content includes the following aspects:（1）The absorption and luminescence characteristics of DAST solution were systematically investigated.The experimental results show that in the visible light band,both the absorption spectra and the emission spectra of the DAST solutions show only one peak.For the absorption spectra,the peak wavelength of DAST will blue-shift as the solvent polarity increases.In the fluorescence spectra,on the contrary,as the solvent polarity increases,the emission peak position red-shifts.In four solvents with different polarities,including deionized water,methanol,ethanol,and isopropanol,DAST shows a large Stokes shift which is positively correlated with the polarity of the solvent.（2）DAST films were prepared by spraying,and the effects of the annealing temperature on the morphology,crystallinity,absorption and fluorescence characteristics of the as-prepared films were investigated.Results show that low-temperature annealing（60^oC）has almost no effect on the morphology and fluorescence characteristics of the film.However,after annealing at a high temperature of 150^oC,the film becomes denser,and a preferential growth along the（004）crystal plane was observed.Moreover,after high-temperature annealing,the absorption spectra and fluorescence emission wavelengths of the DAST films red-shift,and the fluorescence emission peak intensities decrease.The fluorescence emission spectra results also show that two emission peaks were detected from all the DAST films,clearly different from those observed in the DAST solutions.Moreover,it was found that the two fluorescence emission peaks of DAST films are excited by the intramolecular charge transfer from the donor to the acceptor in the cation and the charge transfer from the anion to the cation,respectively.（3）DAST@SiO₂ composite fluorescent microspheres were prepared.Compared with those of the DAST solutions,the emission peaks of the composite microspheres blue-shift for 17-39 nm.Within the tested content range（15-35mg）of DAST,as the DAST content increases,the peak of the composite microspheres will gradually red shift.It shows that the fluorescence can be adjusted by changing the concentration of DAST.Compared with the highest emission intensity of DAST in the corresponding solution,the fluorescence of the DAST@SiO₂ composite microspheres is enhanced by about 54 times in the aqueous solution,or about 10 times in the ethanol solution.（4）Silver nanoparticles（AgNPs）with different contents were further added to the above composite microspheres,by which the plasmon resonance effect was used to further control the fluorescence of DAST.The research results show that for the prepared DAST@SiO₂ composite microspheres,and with the AgNPs particle sizes of 22±7 nm and the concentration of 5.39μg/m L,the fluorescence intensity of the composite microspheres is about 13 times that in the ethanol solution of DAST,and the fluorescence peak is blue-shifted by 34 nm.