Studies On Fluorescence Spectroscopy And Hydrogen Bond Action Mechanism Of Typical Organic Molecules In Aqueous Solution

Based on the techniques of fluorescence spectroscopy, time-correlated single photon counting(TCSPC) and fluorescence polarization, the microstructure and the mechanism of the hydrogen bond of three typical organic molecules (melamine, acetic acid and isopropanol) in aqueous solution are studied. Through the quantum chemistry calculation and fluorescence dynamics process analysis, the spatial structure characteristics of association molecules are obtained.First, the steady fluorescence spectroscopy and time-resolved characteristics of melamine molecule in aqueous solution are studied experimentally. The results show that there are two fluorescence structures in melamine-water solution. The mechanism of fluorescence emission and concentration quenching, the internal relation of relative components concentration and fluorescence lifetime are elucidated. The variations of principal fluorescence peak and relative fluorescence intensity are obtained.Then, the steady and transient fluorescence spectrum and component information of acetic acid-water solution are studied. Three variations of molecular association are obtained in acetic acid-water solution with various volume ratios. The total absorbance and fluorescence emission efficiency of acetic acid-water solution are tested. The association constant and structural characteristics of acetic acid molecules and water molecules through hydrogen bond bridge are determined.Next, the cluster structure characteristics of isopropanol molecule and water molecule association are studied on basis of fluorescence spectroscopy technology. By using derivative analysis and Gaussian decomposition methods for the fluorescence spectra, it indicates that there are7types of luminescent cluster molecules by the action of hydrogen bonds, formed by isopropanol and water molecules in different ways, exist in the solution. The relative spectroscopic line parameters of each cluster are obtained. The variation of relative component content, emission participation concentration and relative fluorescence intensity of each cluster are illustrated. The molecular orientation with characteristic of anisotropy and the excimers with parallel planar structures in isopropanol aqueous solution are revealed.Finally, aiming at the structural characteristics and energy level transition of the three typical organic molecules and water molecule association, the molecular dynamics simulation is carried out by using density functional theory (DFT). The low energy structure acted by different hydrogen bonds of (Melamine)m-(Water)n (m=1-2, n=1-3),(Acetic acid)m-(Water)n (m=1～2, n=1～3) and Isopropanol-(Water)n (n=1～6) are inversed. By studying hydrogen bond length, average bond angle, dihedral angle, energy difference of HOMO and LUMO, the spatial structure information of different physical models are obtained. The electronic energy transfer mechanism of ground-state energy levels is clarified.The research contributes to the study of the hydrogen bond influence mechanism and physicochemical properties of three typical orgnic molecules in aqueous solution. The results can provide reference for the theoretical calculations and application of organic molecules in aqueous solution, especially for the rapid and sensitive detection of melamine relative content in dairy products.