The Dynamics Of Ultrafast Process Of Chlorophyll A In Liquids Studied By Femtosecond Laser

Most chemical reaction and almost all the biological chemical reaction take place in liquid. Studying the ultrafast dynamics of complex molecule in liquid is very important to understand the chemical reaction, the essence of the biological chemical reaction especially closely related to life course.In this thesis, by use of femtosecond time-resolved fluorescence depletion spectroscopy, we study the ultrafast dynamics of Chlorophyll a (Chl a) in solvents. We have observed the internal conversion (IC) of Chl a in solvent, and proved the Foster theory, our results including the deactive mechanism of Chl a are described as follows:After absorbing laser pulse, Chl a molecules could be excited to the higher excited state. Chl a then deactivates to the lowest excited state preceding the act of excitation transfer;the IC time of Chl a in different solvents are different when we use the same wavelength of the exciting laser. The IC time of Chl a in different solvents result from DN and dipole moment of solvent;the IC time of Chl a in same solvent are different when we use the different wavelengths of the exciting laser. It is found that the IC of Chl a from S₄→S₁ in ethyl acetate, dioxane, tetrahydrofyran and acetone, are faster than S₃→S₁, and the IC of Chl a from S₄→S₁ in dimethyl formamide, ethyl ether, cyclohexanone, and pyridine are slower than S₃→S₁. We suggest that there may be different deactive mechanism;the IC of Chl a in alcohol solvents are very fast irrespective the exciting wavelength. It is attributed to the intramolecular hydrogen bond;because the oxygen evolution rate of seedlings grown in blue light is significantly higher than the rate of those grown in red light in photosynthesis,...