Research On Organic Solvent Fluorescence Spectra Induced By UV-Light

Based on the research of the UV-light absorption spectra and the fluorescent spectra of ethanol and acetic acid solutions, the spectral characteristics and the physical mechanisms, as well as the similarities and differences of the two fluorescent spectra are deeply investigated and discussed.Firstly, we employ the exciting light, which has the longest wavelength that can be absorbed by ethanol, to irradiate ethanol solutions to investigate the fluorescent spectra. The relationship between the relative fluorescence intensity and the solution concentration is studied in detail. The results indicate that ethanol molecules can effectively absorb the exciting light with the wavelength of 253.7 nm and they can emit fluorescence with the peak value of 395 nm. The emitting mechanism of ethanol molecule is also discussed and a viewpoint is raised that the non-bonding electrons in O atoms transit as absorbing the exciting light. Then the phenomena that the relative fluorescence intensity changes obviously with the alteration of solutions concentration and the fluorescence quenching are studied.Secondly, the influence on the fluorescence spectra induced by different wavelength UV-light with the wavelength less than 250 nm is investigated. As a whole, there is little difference in the emitted spectrum profiles, however, the center wavelength of the fluorescent spectra are red-shifted distinctly when the photon's energy decreases. It is pointed out that the cause for such phenomena is that the nonbonding electrons transit to different excited single-states after absorbing light with different wavelength. The electrons, which absorb photons with more energy, may transit with larger energy level interval, and thus the emitted photons, which also have larger energy level interval, must have shorter wavelength and vice versa.Lastly, the fluorescent spectra of acetic acid solutions induced by UV-light of 253.7 nm are studied. It is revealed from the experimental results that acetic acid molecules emit fluorescence photons with the wavelength of 395 nm after they absorb excited light. The spectral characteristics of acetic acid solutions with different solution concentration are investigated. A physical mechanism is given that n electrons make a transition of n - * as absorbing exciting light, and the excited electrons are unstable so as to emit fluorescence by radiation when they return to the ground state and the transition type is * - n . It is put forward that the fluorescence dynamic quenching process is resulted from the change of radiation transition to nonradiation transition, and the quenching constant is calculatedaccording to Stem-Volmer equation.The results of this paper will contribute to the study of other organic and biologic molecules fluorescence spectra when acetic acid and ethanol serve as solute and solvent, and what's more, they will offer theoretical foundation for fluorescence quenching influence; the results also lay a solid foundation for acetic acid and ethanol appliance and diagnosis technique in experiment and theory.