Study of the contact charge transfer behavior between cryptophanes (A and E) and fullerene by absorption, fluorescence and 1H NMR spectroscopy

A group of novel cage-like compounds cryptophanes A and E were synthesized from vanillin by a three-step method. The intermolecular interaction between cryptophanes (A and E) and fullerene (C60) was investigated in detail by absorption, fluorescence and 1H NMR spectroscopy. The absorption of C60 at 410-650 nm decreased in the presence of cryptophanes A or E. The decrease in absorption intensity was proportional to the concentration of cryptophanes A or E. On the other hand, the fluorescence intensity of cryptophanes A or E decreased and the emission maxima were blue-shifted with the increase in C60 concentration. These results suggest that contact charge transfer (CCT) complexes can be formed from C60 with cryptophanes A or E. In addition, the electrochemical behavior of cryptophanes (A and E) and C60 was studied by cyclic voltammetry. The redox currents of cryptophanes (A and E) decreased and the peak potentials were shifted on addition of C60. The changes in the chemical shifts (Δδ) of aromatic protons of cryptophanes (A and E) in their NMR spectra further support that CCT complexes were formed with cryptophanes as the electron donors and C60 as the electron acceptor.