Rotational Dynamics of DCM in _-CD
The best experimental model for the data involved two rotating spheres each assigned to one of the fluorescence lifetimes.
In 0.132 M _-CD, free DCM had a rotational correlation time (RCT) of 0.059 ns. Bound DCM had a RCT of 0.515 ns.
When in solution with 0.014 M _-CD, free DCM had a RCT of 0.153 ns. Bound DCM had a RCT of 1.28 ns.
In both cases, the RCT for bound DCM is greater than free DCM. As the DCM forms a complex with the CDs, the volume of the rotating species increases and the molecule rotates slower. The slower rotation results in a longer RCT.