Caging anionic structure of a proton transfer dye in a hydrophobic nanocavity with a cooperative H-bonding

We report on UV-vis absorption and emission studies of 3-hydroxyflavone (3HF) complexed to cyclodextrins (CD). The results show a stabilization of a caged anion through a proton-transfer reaction and inclusion of 3HF into CD. The cooperative H-bonding network of CD plays a central role in the deprotonation of the guest. Picosecond fluorescence measurements of the confined structure suggest no zwitterionic species formation of 3HF within the nanocage. Time-resolved emission anisotropy experiment on the complexes shows a large degree of confinement of the nanostructure. The specific and no specific interactions between the guest and the host observed here are reminiscent to many phenomena found in enzymatic reactions where hydrophobic as well as hydrophilic effects play a key role in biochemistry. (c) 2005 Elsevier B.V. All rights reserved.