The synthesis o f three dansyl appended cyclodextrin derivatives, differing in the spacer length between cyclodextrin and the dansyl moiety, is described. In compound 4 the fluorophore is directly attached to the cyclodextrin. Com pound 5 contains an ethyl spacer and compound 6 a triethylene glycol spacer. These com pounds are designed to detect neutral organic guest molecules like cyclohexanol and adamantanecarboxylic acid in water by fluorescence spectroscopy. At neutral pH none of the compounds is sensitive towards guest molecules. For compound 4 this is due to the fact that the dansyl group is located outside the cyclodextrin cavity. For compunds 5 and 6 the low sensitivity is the result o f a strong self inclusion o f the dansyl group. Lowering the pH results in protonation o f the dimethylamino group o f the dansyl moiety, which makes the self-inclusion less favourable leading to a strongly increased response towards guests. This phenomenon allows the sensors to be switched on and off by lowering or increasing the pH o f the solution. Compound 6 is able to detect adamantanecarboxylic acid at 5 x 10' 7 m ol" 1 dm 3 concentration at pH 1.