Complexation and Fluorescence of Tricyclic Basic Dyes Encapsulated in Cucurbiturils

Abstract

Tricyclic basic dyes (proflavine, acridine orange, pyronine, pyronine Y, oxonine, thionine and methylene blue) often form one-to-one or two-to-one complexes with CB[7] and CB[8], respectively. In the case of pyronine Y, the complexes with CB[7] and CB[8] have a one-to-one and three-to-one stoichiometry, respectively. The binding constants for CB[7] complexes range from 3.07x10(6) to 1.70x10(7) m(-1). In the case of CB[8], the association constant varies between 3.24x10(13) and 2.50x10(16) m(-2). Overall, these binding constants are four orders of magnitude higher than those reported for the same dyes in beta and gamma-cyclodextrins. Formation of the host-guest complexes leads to an increase in the fluorescence quantum yields in the case of CB[7], while the dimeric or trimeric dye encapsulated in CB[8] are remarkably less fluorescent than the same dye in diluted solutions.