DIFFERENTIAL ANISOTROPY OF POLARIZABILITY MEASURED BY PICOSECOND TRANSIENT DICHROISM AND BIREFRINGENCE

The difference in the anisotropy of the polarizability between ground and excited states for two dyes in ethanol was first directly measured by Waldeck et al. using transient molecular dichroism and the birefringence method. In this paper, we present the development of the theoretical description of this method and we measure the differential polarizability for the dyes DODCI, sulforhodamine 101, and nile blue in various alcohols. The following values were obtained: < + 200 Å3, + 590 Å3, and + 720 Å3, respectively, independent of the solvent. The proposed theory was used in a computer simulation and good agreement of the observed and calculated values was obtained. In the experiment, the rotational relaxation times were also determined and compared to the results obtained for the same molecules from the measurements using the up-conversion technique. The difference in measured rotational times for dyes in more viscous alcohols using both experimental techniques suggests that the rotational diffusion is different in the ground and excited states. © 1990 American Institute of Physics.