Ultrafast Vibrational and Thermal Relaxation of Dye Molecules in Solutions

Abstract

Intra-and intermolecular relaxations of dye molecules are studied after the excitation to the high-lying excited states by a femtosecond laser pulse, using femtosecond time-resolved stimulated emission pumping fluorescence depletion spectroscopy (FS TR SEP FD). The biexponential decays indicate a rapid intramolecular vibrational redistribution (IVR) depopulation followed by a slower process, which was contributed by the energy transfer to the solvents and the solvation of the excited solutes. The time constants of IVR in both oxazine 750 and rhodamine 700 are at the 290-360 fs range, which are insensitive to the characters of solvents. The solvation of the excited solutes and the cooling of the hot solute molecules by collisional energy transfer to the surrounding takes place in the several picoseconds that strongly depend on the properties of solvents. The difference of Lewis basicity and states density of solvents is a possible reason to explain this solvent dependence. The more basic the solvent is, which means the more interaction between the solute and the neighboring solvent shell, the more rapid the intermolecular vibrational excess energy transfer from the solute to the surroundings and the solvation of the solutes are. The higher the states density of the solvent is, the more favorable the energy transfer between the solute and solvent molecules is.

Theoretical analysis of femtosecond fluorescence depletion spectra and vibrational relaxations of dye oxazine 750 and rhodamine 700 molecules in acetone solution

“…The influences of laser pulse and molecular structure parameters on the FDSs are also investigated. The calculated FDSs agree well with the experimental results of Liu et al [18,19].…”

“…Many experimental techniques, such as fluorescence upconversion [1][2][3][4][5][6], femtosecond photon echo [7], two-step excitation [8], time-resolved fluorescence Stokes shifts [9], time-resolved spontaneous emission spectra [10 -15], and femtosecond time-resolved stimulated emission pumping fluorescence depletion spectrum [16,17], have been developed to measure the vibrational relaxation and the solvent effects of mole-cules in solution. Liu et al [18,19] measured experimentally the femtosecond fluorescence depletion spectra (FDSs) of dye molecules in solution and studied the relaxation dynamics of dye molecules. Theoretically, Lin and coworkers [20] studied the effect of vibrational relaxation on the pump-probe stimulated emission and calculated the time constant of vibrational relaxation of Rhodobacter capsulatus.…”

Thermal Characterization of ZnO-DMSO (Dimethyl Sulfoxide) Colloidal Dispersions Using the Inverse Photopyroelectric Technique

“…We have used Cbf = 2.00 ± 0.03 J cm -3 K -1 for the specific heat capacity of DMSO. 17 From our measured value of ebf = (0.033 ± 0.001)¥ 10 -3 J cm -3 K -1 s -1/2 (the same value was obtained for both, DMSO and DMSO + 3% water using nanopure water as a reference sample), we can obtain using Eq. (5) the values of enf for the different concentrations.…”

Photo-induced intramolecular charge transfer from antenna to anchor groups in phenoxazine dyes

“…The polarization of the probe beam with respect to the polarization of the pump beam was adjusted to the magic angle to avoid reorientation effects [13]. The transient absorbance profiles were fitted using the following model function [Eq.…”