External heavy atom effects of 6-deoxy-6-iodo-α-cyclodextrin on the room-temperature phosphorescence of 6-bromo-2-naphthol and 3-bromoquinoline in aqueous solutions

6-Deoxy-6-iodo-alpha-cyclodextrin (alpha-CDI) has been found to form a 1:1 inclusion complex with 6-bromo-2-naphthol. A further association occurs between the 1:1 inclusion complex and an additional alpha-CDI molecule, leading to the formation of a 2:1 alpha-CDI-6-bromo-2-naphthol inclusion complex. The room-temperature phosphorescence of 6-bromo-2-naphthol is observed from the 2:1 alpha-CDI-6-bromo-2-naphthol inclusion complex, whereas the 1:1 inclusion complex does not emit it. The room-temperature phosphorescence intensity for the 2:1 alpha-CDI-6-bromo-2-naphthol inclusion complex is reduced by about 18% relative to that for the 2:1 inclusion complex composed of the parent alpha-CD, indicating the external heavy atom effects of alpha-CDI on the bound guest. The external heavy atom effects of alpha-CDI have also been examined on the room-temperature phosphorescence intensity of 3-bromoquinoline buried within the alpha-CDI cavity. At the same CD concentrations (2.0 X 10(-3) mol dm(-3)), the room-temperature phosphorescence for alpha-CDI has been decreased by about 10% relative to that for alpha-CD. (C) 1998 Elsevier Science S.A.