Fluorescence Properties Of Thio-functionalized Ionic Liquids

In recent years, the studies of luminescent properties of room temperature ionic liquids(RTILs) have attracted the interests from researchers. However, the researches are mainly focused on theluminescent properties of imidazolium-based ILs whose anion is [PF6]-or [BF4]-up to now. These ILs arepoor chemical stability in water, which limits their practical applications. In this paper, several kinds ofthiol-functionalized ionic liquids have been synthesized based on quaternary ammonium cation andimidazolium cation, and the attempts of the article are to determine the factors affecting fluorescenceintensity, lifetime and quantum yield resulting from the species of cation or anion, solvent, concentration,temperature and so on. This provides experimental data for the application of ILs in biochemistry,fluorescent probes and fluorescent sensor. The main contents of the thesis are as follows:1. Thiol-functionalized ionic liquid based on quaternary ammonium cation, C10H24NS, wassynthesized and characterized by means of FTIR,1HNMR,13CNMR and ESI-MS. Imidazolium-based ionicliquid of [HS-C2mim]NO3was synthesized by the processes reported previously in syntheses of[HS-C4mim]NO3and [HS-C10mim]NO3, and the desired product was determined by nuclear magneticresonance spectroscopy.2. The fluorescence properties of the quaternary ammonium and imidazolium ILs were studiedwith FLS980multifunctional fluorescence spectrometer. It is shown that fluorescent properties of ILs in thevisible region can be detected from the thiol-functionalized imidazolium cations. This is ascribed to theunpaired electron in the-SH groups conjugated with the imidazolium cation in the neighboring molecule,which reduces the energy of electron transition. Afterwards, the effects of alkyl chain length, excitation wavelength, concentration, solvent, temperature and other conditions on the fluorescence intensity werediscussed. The maximum emission wavelength of the ILs red-shifts with the excitation wavelength. Thefluorescence intensity of [HS-C4mim]NO3is the strongest among the three kinds of ILs; the fluorescenceintensity of [HS-C2mim]NO3and [HS-C4mim]NO3decline with decreasing the concentration andincreasing solvent polarity, but the phenomenon was not observed from [HS-C10mim]NO3because of theweak fluorescence intensity.3. The excitation wavelength at405nm or475nm is selected as light source to explore theeffects of the alkyl chain length, concentration and solvent on fluorescence lifetime. It is shown that thefluorescence lifetime of [HS-C4mim]NO3has the maximum among these ILs, and that of [HS-C2mim]NO3and [HS-C4mim]NO3decrease with increasing the concentration and solvent polarity, but that of[HS-C10mim]NO3don’t follow it due to the poor fluorescence.4. The fluorescence quantum yields of ILs were measured by the integrating sphere. The purposeis to study the alkyl chain length, concentration and solvent how to influence the quantum yields. Thequantum yield of [HS-C4mim]NO3is15.0%,30times nearly more than that of [C4mim][PF6] well-studiedin the past. The quantum yields of all ILs decline with increasing solvent polarity under the sameexperimental conditions.