Polarized excitation and emission anisotropy decay

the polarized fluorescence decay components contain information about the motional dynamics of the molecule. 

The expected time dependence of the emission anisotropy has been worked out for several important models, including those detailed in the following sections. 

In this case, the time-dependent fluorescence anisotropy is given by 

3 Rod-shaped molecule with restricted motion For a rod-shaped molecule with its transition dipole moment oriented along the rod s long axis and whose motion is confined to a cone, with one end of the rod fixed at the cone s apex, the emission anisotropy is given by 

Because the molecule s motion is restricted, the anisotropy does not decay to zero but reaches some final constant value, r . Equation 19 is typically used to model the anisotropy decay of a rod-shaped fluorophore such as l- 4-trimethylammomumphenyl)-6-phenyl-l,3,5-hexatriene (TMA-DPH) embedded in a phospholipid membrane, where it reports on the order and dynamics of the latter. The so-called order parameter S of the membrane is defined as 

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