The Ultrafast Dynamics of the Dye Molecules in Liquids Studied by Femtosecond Laser
|School||Dalian Institute of Chemical Physics|
|Course||Physical and chemical|
|Keywords||fluorescence depletion charge transfer solvation intramolecular vibrational redistribution femtosecond laser|
The ultrafast dynamics of a near-infrared heptamethine cyanine dye and Oxazine 750 laser dye have been studied in different solvents using the femtosecond time-resolved stimulated emission pumping fluorescence depletion (FS TR SEP FD) technique. The dynamical constants of the intramolecular vibrational redistribution (IVR) and the solvation process are observed. Moreover, the charge transfer mechanism of the heptamethine cyanine dye has been further studied during the excitation and new conclusions are obtained.The charge transfer mechanism of the heptamethine cyanine dye has been studied with 3D real space analysis method: the electrons can transfer from the sulfonate (-SO3-) groups to the bridgehead amine and the electron-defect conjugated system. And the absorption and fluorescence spectra of the ICT state in alcoholic and aprotic solvents are fitted successfully by Kamlet and Taft(π*,α,β) scale. The effects of the hydrogen bonding interactions between the solute and solvent to the charge transfer process and the change of the dipole moment between the ground and excited states are discussed.The ultrafast dynamics of the heptamethine cyanine dye has been studied in the alcoholic and aprotic solvents using the femtosecond time-resolved stimulated emission pumping fluorescence depletion (FS TR SEP FD) technique. The faster decay on the hundreds of the femtosecond time scale and the slower decay on the order of picosecond are found. The intramolecular vibrational redistribution (IVR) and the ultrafast solvent inertial or librational relaxation of solvation should account for the faster decay, while the slower decay is attributed to the diffusive solvent relaxation. The time constants of the slower decay increase with the hydrogen-bonding energy in alcoholic solvent because the hydrogen bond inalcoholic solvent hinders the rearrangement of the solvent. The time constants of the slower decay decrease with the dipole moments of the aprotic solvent molecules due to the interactions between the aprotic molecules and the excited dye molecule.We have been used the FS TR SEP FD technique to study the ultrafast dynamics of the Oxazine laser dye in the alcoholic solvents. The conclusions are similar to those of the heptamethine cyanine dye in the alcoholic solvents.