The Experimental Investigation On Ultrafast Dynamics Of Coumarin C540A In Different Solvents

With the rapid development of laser technology, laser power is increasing and the pulse width has also been gradually smaller. The molecules will be motivated to the first or second electronic excited states with different rotation or vibration level from the ground states under the incident photon. But the lifetime of the excited states is very short and the electrons will back to the ground states within 10- 1 4-10- 9s. The emergence of femtosecond laser provides the probability for the study of ultrafast molecular dynamics especially in liquid phase system, such as the redistribution of internal energy of excited state, charge transfer, solvent effects and so on. Nowadays, the main femtosecond time-resolved spectroscopic techniques include femtosecond pump-probe, femtosecond fluorescence up-conversion, and femtosecond fluorescence depletion. At the same time, because the dye molecules have the characteristics of high luminous efficiency, low cost, wide variety and other characteristics, they are widely used to study ultrafast dynamics of liquid-phase system.In this paper, by using femtosecond fluorescence up-conversion, the dynamics process of coumarin C540 A molecular in solvent ethanol, acetic acid and dimethyl sulfoxide was systematically studied.This dissertation consists of five chapters.Chapter 1 described the development and the principle of the laser firstly, then, several ultrafast process in the liquid phase system was introduced, finally, the research status of dye molecules and the significance of the topic in this paper was also presented.Chapter 2 introduced three main technology of the time-resolved spectroscopy: femtosecond pump-probe, fluorescence up-conversion, and fluorescence depletion.Chapter 3, the experiment part, the femtosecond laser system and the principle of fluorescence up-conversion experiment device was described in detail.Chapter 4, the ultrafast dynamics of coumarin C540 A molecular in three kinds of solvents was systematically studied. Experimental results shows that the concentration does not change the structure of the molecule fluorescence spectrum, but with the polarity of the solvent increases, the fluorescence spectrum has the phenomenon of red shift, and time constant of ultrafast intramolecular corresponding is also increases. Hydrogen bonding of solvent will accelerate internal energy redistribution of molecules excited states(IVR), while prevent the solvation of the ICT states.Chapter 5, the Summary and outlook.