Inclusion of 2-chloronaphthalene by alpha-cyclodextrin and room-temperature phosphorescence of 2-chloronaphthalene in aqueous D-glucose solutions containing alpha-cyclodextrin

In aqueous solutions, alpha-cyclodextrin (alpha-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 alpha-CD-2-CN inclusion complex. In aqueous D-glucose solutions, alpha-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 alpha-CD, the room-temperature phosphorescence of 2-CN has been observed. The 2:1 alpha-CD-2-CN inclusion complex is responsible for the room-temperature phosphorescence. The quantum yield (phi(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 phi(p) value of 2-CN in ethanol at 77 K. When KI is added to D-glucose solutions containing alpha-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 alpha-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.