Rotational relaxation dynamics of a β-carboline analogue in cyclodextrin nanocavity: How does the cavity size barricade the molecular rotation?

In the present work the rotational dynamics of a polarity sensitive biologically active β-carboline derivative, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), have been discussed in three native cyclodextrin environments using ultrafast time-resolved fluorescence technique. AODIQ exhibited bi-exponential anisotropy decay in the cyclodextrin environments. The rotational motion of the probe was interpreted on the basis of two independent motion; local (internal motion of the guest within the aggregate) and global (overall rotational tumbling of the complexes). It is found that the cyclodextrin environment causes significant retardation of rotational motion of the probe. Experimental results reveal that relative host–guest size determines the character of the intermolecular host–guest dynamics.