Investigation of orientational randomization during nonradiative decay of excited-state dye molecules in a solvent

A recent investigation [1] studied rotational dynamics of dye molecules in an isotropic liquid crystalline solvent and found evidence that the orientation of electronic-excited-state dye molecules randomize to a large extent as they decay nonradiatively to the ground state via solute/solvent interaction. This loss of orientational order through nonradiative relaxation is of fundamental importance but has hardly been studied previously. We have carried out a transient dichroism experiment that has improved accuracy compared to Ref. [1] to measure quantitatively the extent of orientational randomization of excited dye molecules undergoing nonradiative decay. A comparison of the effect between different solute/solvent systems was also carried out. Work Supported by NSF