EXCITED-STATE PROTON-TRANSFER OF 2-NAPHTHOL INCLUSION COMPLEXES WITH CYCLODEXTRINS

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 ti me-resolved optical spectroscopy techniques, are related to the comple xation constants of the two protolytic forms: as the standard free ene rgy of inclusion is larger for the molecular form than for the ion, th is aromatic acid becomes less acidic upon complexation. Excitation eff ects relative to the ground state are discussed with respect to spectr al shifts. In the case of alpha-cyclodextrin as host, 1:2 guest:host c omplexation suppresses excited-state deprotonation. The variation of t he microenvironment and its implications on dissociation and recombina tion rates are discussed. The experimental results are interpreted on the basis of structural models for these complexes, obtained from mole cular modeling techniques.