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-triplet intersystem crossing, which decreases with increasing polarity, was found to be a good indicator of nonspecific solvent-solute interactions, while the rate of direct internal conversion from the singlet excited state was correlated with hydrogen bonding. The fast internal conversion of singlet excited fluorenone/beta-cyclodextrin complexes shows that the probe molecule, while embedded within the cyclodextrin cavity, still remains hydrogen bonded.