Binding studies between tetrathiafulvalene derivatives and cyclobis(paraquat-p-phenylene)

The complexation between a number of different π-electron donating TTF derivatives and the π-electron accepting tetracationic cyclophane cyclobis(paraquat-p-phenylene) (CBPQT⁴⁺) has been studied by ¹H NMR and UV-vis spectroscopy. The results demonstrate that the strength of association between the donors (TTF derivatives) and acceptor (CBPQT⁴⁺) is strongly dependent on the π-electron donating properties (measured by the first redox potential E_1/2¹) of the TTF derivatives. However, the first redox potential (E_1/2¹) is not the only factor of importance. The extended π-surface of the TTF derivatives also exerts a stabilizing influence upon complexation. The kinetics for the complexation-decomplexation were studied using ¹H NMR spectroscopy and are related to the bulkiness of the TTF derivatives. These effects may serve to improve the design of interlocked molecular systems, especially (bistable) molecular switches, in which CBPQT⁴⁺ and a derivatized TTF unit are incorporated.