SOLVENT-DEPENDENT RADIATIONLESS TRANSITIONS IN FLUORENONE - A PROBE FOR HYDROGEN-BONDING INTERACTIONS IN THE CYCLODEXTRIN CAVITY

Fluorescence lifetimes, fluorescence quantum yields and triplet yields were measured for fluorenone in various hydroxylic and non-hydroxylic solvents, and in beta-cyclodextrin complexes. The rate of singlet-tri plet intersystem crossing, which decreases with increasing polarity, w as found to be a good indicator of nonspecific solvent-solute interact ions, while the rate of direct internal conversion from the singlet ex cited state was correlated with hydrogen bonding. The fast internal co nversion of singlet excited fluorenone/beta-cyclodextrin complexes sho ws that the probe molecule, while embedded within the cyclodextrin cav ity, still remains hydrogen bonded.