We report on emission studies of excited phototautomers of 1'-hydroxy-2'-acetonaphthone in aqueous solutions of alpha-cyclodextrin (alpha-CD). Caging by alpha-CD provokes a similar to40 nm blue shift of the emission, and increases the emission lifetime from 90 ps to 1 ns. The rotational time of the caged phototautomers varies from 50 to 180 ps, while that of global rotational time of 1:2 complex (HAN:(alpha-CD)(2)) is similar to950 ps. These results are explained on the basis of confinement effects on the twisting motion of the formed phototautomers within the cavities provided by one or two CD. (C) 2003 Elsevier Science B.V. All rights reserved.