Complexation of Triptycene-Derived Macrotricyclic Host with pi-Extended Viologens

Development of novel macrocyclic hosts with the capability of binding selected substrates in specific complexation modes is always a very important and attractive topic in host-guest chemistry. Recently, we reported a novel macrotricyclic polyether containing two triptycene skeletons with rigid structure and two dibenzo-30-crown-10 moieties, which could show wide complexation abilities toward different kinds of guests. It was found that depending on the guests with different terminal functional groups and structures, the macrotricyclic polyether could form 1: 1 or 1: 2 complexes with the guests in different complexation modes in solution and also in the solid state. Moreover, the conformation of the macrocycle could easily be adjusted by the different encapsulated guests, which was to some extent similar to substrate induced fit of enzymes. It was also known that viologens with reversible single electron-accepting ability were usually used for the basic study of electrochemical and photoelectrochemical processes. They have also been widely utilized as electron deficient guests for host-guest chemistry. Compared with the viologens, pi-extended viologens with conjugated structures have much more rich redox behaviors, and they could be used for photolithography, a source of electric oscillations, molecular electronic devices, and also as agents for charge transport across vesicles. However, the applications of pi-extended viologens as guests in host-guest chemistry are still very limited. In this paper, complexation between the triptycene-derived macrotricyclic host and pi-extended viologens in both solution and solid state was investigated in detail. It was found that depending on the guests with different linker-species and terminal functional groups, the macrotricyclic host could form 1 : 1 or 1 : 2 complexes with the guests in solution. Besides the 1 : 1 or 1 : 2 complexes, the macrotricyclic host could also form supramolecular poly[3]pseudorotaxane-type complexes with the guests in different complexation modes in the solid state. Formation of the complexes was proved by the H-1 NMR, ESI-MS spectra, and X-ray crystal structures.