Design And Application Of The Optical Transient Absorption Test System

The system of the optical transient absorption is powerful in studying the dynamics of energy transduction and charge transfer processes in biological and chemical samples, as well as in photo-electrical material. The optical transient absorption Spectra is one of the powerful techniques that can probe the fast reactions at room temperature and has already been used in different research fields. From acquiring the direct spectroscopic information of different excited states and transient intermediates, we can investigate the photo-physical and photo-chemical process of bio-molecules, or instantaneous molecules and polymer in the condensed phase.Combining the laser induced transient absorption spectra acquired by our homemade nanosecond laser flash photolysis instrument, we researched the whole systems with different lamps and other detective methods. Specific work can be divided into the following four parts:The first part, the sample system was excited by the laser pulse with a certain intensity. A large number of electronic excited states and other elements of transient intermediates were generated by the photo-physical or photochemical process. Another detect light with continuous spectra is perpendicular to the excited laser through samples. The concentration of the transient intermediates produced by the excitation was changed according to the time. This will inevitably cause the transmission light intensity of the analysis light to change corresponding to the time. The photo-detector convert the change of such intensity into the change of electrical signals .Then changes were recorded by the oscilloscope. The curve obtained from the oscilloscope will be corresponding to the changes of the concentration of transient intermediates. The results also recorded the reaction process and the life of the transient species. Finally we measured in different wavelengths and can acquire the time-resolved absorptionspectroscopy. Based on the study of spectrum, the components and technology requirement of the optical transient absorption Spectra were present.The second part, the first nanosecond laser-induced transient absorption spectroscopy instrument was carried out. The system composing mainly by the He-Ne laser, photodiode and oscilloscope is to obtain the optical transient absorption Spectra. In this thesis, the concept and technical plan for the reconstruction of the optical transient absorption spectra are discussed. Through a complete study based on theory of original design, some fetal drawbacks were pointed out for the original design of the optical transient absorption spectra. Then on the prerequisite to retain the original design, a renewed design was put forward, which used the monochromator to analyze samples for the detection of different wavelengths of transient absorption spectra. We have decided to adopt a xenon lamp with continuous spectrum as the light source instead of the He-Ne laser. The computer-controlled monochromator can obtain light with a signal wavelength of the xenon lamp. Meantime, a detective module of APD with high sensitivity, high gain and a frequency bandwidth of DC to 10M was used as a detector in order to analyze samples for the detection of different wavelengths of transient absorption spectra. In the meanwhile, a new experimental instrument for transient absorption spectra was designed and constructed, which is more reasonable and easier to us. We used the optical fibre lamp as the detect lamp instead of the xenon lamp in the second system .This lamp is smaller than the xenon lamp, more simple to operate with less heat.The third part, the light source and detector can be changed according to each experiment. Output signals of the detector are amplified by a current amplifier and then be collected by a oscilloscope .After beingtransferred to digital signals, the data finally come out in the form of curves. After the computer processing with the soft of Microcal Origin7.5, we obtain the transient absorption Spectra as the function of time. Global analysis of the experiment system, including each part's design concept and realization, is presented in this paper on the base of the principles of the monochromator and photoelectric detector and at the same time the method of measuring each parameter is emphasized, it is ended by a group of results at different wavelengths and different samplings of the average curve, background noise curve and the absorption curve.The forth part, in this paper, the optical transient absorption spectra technique was used to investigate the transient absorption spectra of Erythrosine B, which are phosphorescent probes and photo-sensitizers. The excited states and transient intermediates of Erythrosine B were explored. The kinetics and mechanisms involving Erythrosine B were studied. The transient absorption spectroscopic of Erythrosine B in H2 O solution upon pulse excitation at 532 nm displays two bands at 550 nm and 600 nm respectively. In addition to get better absorption and the longer the life expectancy of transient species, we also designed a cycle of the sample pool to remove the oxygen and reduce oxygen quenching the triplet state.