1:1:1 Inclusion Compounds of β-Cyclodextrin with Fluorene and Alcohols or Nitriles in Aqueous Solution

Fluorene forms a 1:1 inclusion compound (FC) with β-cyclodextrin (CDx) in aqueous solution. From electronic absorption and emission spectra, FC has been found to further associate with alcohol (from ethanol to 1-pentanol) or nitrile (from propionitrile to hexanenitrile) to form a 1:1:1 inclusion compound. An equilibrium constant (K3) for the formation of the 1:1:1 inclusion compound from FC and alcohol, and that (K4) from fluorene and a 1:1 inclusion compound of CDx with alcohol have been determined. Upon going from ethanol to 1-pentanol, the value of K4 increases, reaches a maximum at 1-propanol, and then decreases while K3 monotonously increases with an increase in the alkyl-chain length of alcohol. For nitriles, K3 and K4 have also been evaluated. In this case, the largest K4 value is seen for propionitrile and butyronitrile, while K3 increases with increasing the alkyl-chain length of nitrile.