Ultrafast Time-resolved Spectroscopy Of Dye Molecules In Reverse Micelles

Ultrafast time-resolved spectroscopy has become an important method of detecting intramolecular and intermolecular mechanisms and kinetic processes.It is particularly important to optimize this measurement to get better experimental data.In this paper,we have constructed two sets of femtosecond time resolution systems,optical kerr system and transient absorption system.And the kinetic process of the excited state of the dye molecules in the reverse micelles was measured by them.The reverse micelle is a system of nanoscale order,which is similar to molecular layer of the lipid-water interface structure.And the reverse micelle is a kind of oil(nonpolar solution)contain water(polar solution)type colloidal dispersion system,formed by the spontaneous arrangement of nanometer sized "ponds" in the nonpolar solvent,which provides an excellent microreaction space for the preparation of nanoparticles.As a result of the reverse micellar method,the reaction vessel with the order of nanometer size has the advantages of homogeneousness and controllability of particle size,aroused great interest.In this paper,the excited kinetic process and the fluorescence mechanism of the dye molecules C153 and DCM were studied by using ultrafast time resolution spectroscopy as the detection method when the dye molecules were placed in the nanometer sized reaction cell.In the experiments of the optical Kerr system,we studied the chirp characteristics of white light and compared the efficiency and the response time of three different kinds of nonlinear Kerr media(liquid: benzene,CS2;crystal: GGG)to determine the most suitable Kerr medium.The frequency chirp of continuous light is proved to be generated by white light through the Kerr medium.After analysis,it is proved that benzene is the most suitable Kerr medium in these three media.In the experiment of transient absorption,we used surfactants AOT(sodium bis(2-ethylhexyl)sulfosuccinate)and measured the steady-state absorption spectra,fluorescence spectra,transient absorption spectra of coumarin 153 and DCM in the reverse micelles of methanol / AOT / n-heptane.The results show that with the increase of the size of the reverse micelles,steady-state absorption spectra and fluorescence spectra of dye molecule coumarin 153 and DCM have undergone Stokes shift.From the transient absorption spectrum,it is observed that with the increase of the delay time,the larger size of reverse micelles is,the more obvious red shift of central wavelength of the absorption band and emission band are.The red shift of the steady-state absorption spectra and the emission spectra are due to the increase of the number of methanol molecules in the micelles and the formation of the hydrogen bond network.It can be seen that the decay of DCM in the confined domain of the reverse micelles is much slower than not in the reverse micelles from the anisotropic decay diagram of DCM.This is due to the fact that some of the DCM dye molecules are dissolved in the methanol in the micellar interface of reverse micelles and partially are dissolved in the internal micelles of the micelles.The combination of methanol and the head group of AOT in the reverse micelle resulted in an increase of the "viscosity" of the whole environment,and the molecular rotation of the DCM dye molecules in the confined environment was affected by the weak interaction,so that the anisotropy decay in reverse micelles is much slower than in the methanol solution.