Spectral modulation of charge transfer fluorescence probe encapsulated inside aqueous and non-aqueous β-cyclodextrin nanocavities

In this work, we report the spectral modulations of a intramolecular charge transfer (ICT) molecule ethyl ester of N,N-dimethylaminonaphthyl-(acrylic)-acid (EDMANA) when encapsulated in the water and N,N-dimethylformamide (DMF) solution of beta-CD nanocavities. From the nature of the Benesi-Hildebrand (B-H) plots, the stoichiometry of the host guest inclusion complexes are found to be 1:1 in water beta-CD solution and both 1:1 and 1:2 in DMF beta-CD solution. The preferential location and difference in orientation of EDMANA molecule inside the beta-CD cavity has been accessed by analysis of the effect of acid and metal cation Ni2+ on the spectral characteristics in both the media. In case of 1:1 complex, the polar donor group prefers to expose to bulk aqueous phase capable of binding with H+ and Ni2+ ions and the acceptor to the hydrophobic interior. On the other hand, the acceptor group remains exposed to the non-polar bulk phase and the donor group is orientated preferentially inside the non-polar core in 1:2 inclusion complexes. (C) 2009 Elsevier B.V. All rights reserved.