Dansyl-modified cyclodextrins as fluorescent chemosensors for molecular recognition

α-, β-, and γ-cyclodextrin derivatives (cyclodextrin is abbreviated as CD, hereafter) bearing an dansyl or dansylglycine moiety at the primary or secondary side of CD were synthesized as fluorescent indicators for molecular recognition. The CDs with the moiety at the secondary hydroxy side have an asymmetric cavity with a distorted CD framework because of the conversion of one glucose member to an altrose residue and the effects of this distortion of the CD ring on the sensing abilities were examined, compared with the case of symmetrical CDs bearing the dansyl moiety at the primary side. The results demonstrate that the asymmetrical CDs are unfavorable to accommodate the guest species due to the cavity narrowed by the distortion, contrasting with the observation that the symmetrical CDs exhibit remarkable sensing abilities for various guests.