Molecular modeling calculations were optimized at the B3LYP/6-31G(d) (Lee et al., 1988) level of density functional theory (Becke, 1988) using the Gaussian 03 program. Results confirmed the partial inclusion of COP in the hydrophobic cavity of CB[7] (Fig. 3a). In the energy-minimized structure, the methylenedioxyisoquinoline moiety is embedded in CB[7], and the heterocyclic nitrogen is located in the vicinity of a carbonyl-laced portal. The partial immersion of COP in the hydrophobic cavity of CB[7] reduces interaction with water and the degree of freedom of motion of the guest molecule. This state results in a less polar microenvironment which, in turn, leads to fluorescence enhancement. When PQ wasadded to the host-guest system of CB[7]COP, COP and PQ competed to occupy the CB[7] cavity. Some parts of the COP molecule were expelled from the CB[7] cavity upon the introduction of PQ. The energyminimized structure of the CB[7]-PQ complex is shown in Fig. 3b.