Femtosecond time-resolved fluorescence depletion spectroscopy was used in the study of the orientation relaxation of Rhodamine 700(LD700) and Oxazine 750(OX750) in DMSO. The anisotropy functions of the dye molecules were obtained from the fluorescence depletion spectra, as the polarization of probe pulse is parallel and perpendicular respectively. The results show that the transition dipole moment of the pump and the probe of LD700 and OX750 are parallel. The time constants of the orientation relaxation of these dye molecules in DMSO are 1.8 and 1.9 ps for LD700 and OX750, respectively.
