Ground- and excited-state acid-base properties of 2-naphthol inclusion complexes with alpha-, beta-, and some substituted beta-cyclodextrins were studied. Ionization constants, determined by steady-state and time-resolved optical spectroscopy techniques, are related to the complexation constants of the two protolytic forms : as the standard free energy of inclusion is larger for the molecular form than for the ion, this aromatic acid becomes less acidic upon complexation. Excitation effects relative to the ground state are discussed with respect to spectral shifts. In the case of alpha-cyclodextrin as host, 1:2 guest:host complexation suppresses excited-state deprotonation. The variation of the microenvironment and its implications on dissociation and recombination rates are discussed. The experimental results are interpreted on the basis of structural models for these complexes, obtained from molecular modeling techniques.