Inclusion of 2-Chloronaphthalene by α-Cyclodextrin and Room-Temperature Phosphorescence of 2-Chloronaphthalene in Aqueous d -Glucose Solutions Containing α-Cyclodextrin

In aqueous solutions, α-cyclodextrin (α-CD) forms a 1:1 inclusion complex with 2-chloronaphthalene (2-CN), and further associates with the 1:1 inclusion complex to form a 2:1 α-CD−2-CN inclusion complex. In aqueous d -glucose solutions, α-CD also forms the 1:1 and 2:1 inclusion complexes with 2-CN. Equilibrium constants for the formation of the 1:1 and 2:1 inclusion complexes have been evaluated from simulations of the observed fluorescence intensities of 2-CN in aqueous solutions with and without d -glucose. For 2-CN solutions containing both d -glucose and α-CD, the room-temperature phosphorescence of 2-CN has been observed. The 2:1 α-CD−2-CN inclusion complex is responsible for the room-temperature phosphorescence. The quantum yield ( φ p ) of the room-temperature phosphorescence from the 2:1 inclusion complex has been determined to be at least 0.029, which is 19% of a φ p value of 2-CN in ethanol at 77 K. When KI is added to d -glucose solutions containing α-CD, the room-temperature phosphorescence intensity is initially enhanced, but it is decreased with a further increase in the KI concentration. The initial enhancement of the room-temperature phosphorescence intensity is due to the formation of an α-CD−2-CN−I - inclusion complex, and the intensity reduction at higher concentrations of KI seems to be due to the formation of a nonphosphorescent ternary inclusion complex containing two I - ions.