Fluorescence Analysis Of Molecular Association Of Acetic Acid

The fluorescence spectra of acetic acid-water solution excited by UV-light are studied experimentally and theoretically, the relationship between the fluorescence spectra and the molecular association of acetic acid is discussed as well.The fluorescence properties of acetic acid-water solutions excited by various UV-light with the wavelength from 240 nm to 300 nm are studied. It shows that the fluorescence spectra of acetic acid-water solutions are observed in case the wavelength of exciting light is longer than 246 nm. There are three characteristic fluorescence peaks in these spectra. Two of them are at 305 nm and 334 nm respectively, and the third one has a slight shift to longer wavelength in the range of 315-327 nm as the wavelength of exciting light increases. The optimal wavelengths for these three fluorescence peaks are obtained through the measurements of their excitation spectra respectively.The fluorescence spectra of acetic acid-water solutions with various solution concentrations are obtained, and the relationship between fluorescence properties and concentrations of acetic acid-water solutions are studied. It is suggested that the variation in fluorescence spectra with the alteration of solution concentrations is primarily attributed to changes of molecular associations of acetic acid in aqueous solutions. In the case of different solution concentrations, various molecular associations of acetic acid are formed by hydrogen-bond reactions between acetic acid and water molecules, which correspond to different molar absorption coefficients and fluorescence quantum yields. Therefore, fluorescence intensity changes with the alteration of solution concentration. The experimental data also shows that the energy gap for electron transition of acetic acid molecules does not change in various molecular associations.In this paper, the molecular association of acetic acid is investigated using the method of fluorescence analysis. The results offer experimental foundation and reference to studies of molecular association of acetic acid and related area.