Efficient encapsulation of chloroform with cryptophane-M and the formation of exciplex studied by fluorescence spectroscopy.

Efficient encapsulation of small molecules with supermolecules is one of significantly important subjects due to strong application potentials. This article presents the interaction between cryptophane-M and chloroform by fluorescence spectroscopy. The sonicated cryptophane-M solution exhibits light green color in chloroform, and the solid obtained from the evaporation of chloroform also has different color from that of cryptophane-M. In contrast, the sonicated cryptophane-M solutions in other solvents are colorless, and the solid obtained from the evaporation of these solvents has the same color as that of cryptophane-M. Furthermore, the freshly prepared cryptophane-M solution in different solvents is almost colorless, and the solid obtained from the evaporation of these solvents displays the same color as that of cryptophane-M. Although the sonicated cryptophane-M solutions in different solvents have very similar absorption spectra, they exhibit quite different emission spectra in chloroform. In contrast, the freshly-prepared cryptophane-M solutions show similar absorption and emission spectroscopy in various solvents. The variation of the fluorescence spectroscopy in binary solvents with the increasing chloroform ratio suggests that cryptophane-M and chloroform form a 1:1 exciplex, and the binding constant is estimated to be 292.95 M(-1). Although all solvents are able to enter into the cavity of cryptophane-M, only chloroform can stay in the cavity of cryptophane-M for a while, which is mostly due to the strong intermolecular interaction between cryptophane-M and chloroform, and this results in the formation of the exciplex between them.