The construction and switching properties of a novel class of molecular shuttles 1 with imine-bonding stations for macrocyclic diamine parts are reported. Studies on dithioacetalized [2]rotaxane 4 with two hydrogen-bonding stations and a masked imine-bonding station showed that protonation of a macrocycle increases the shuttling barrier due to hydrogen-bond formation between NH 3 (+) groups and the TEG-stations. Hydrolysis of the imine-bonds of the imine-bridged molecular shuttles 1b, c with TEG-stations could exclusively give the [2]rotaxane 2b, c.2H (2+), with the macrocycle hydrogen-bonded with the TEG-station. In contrast, 1a without TEG-stations gave an equilibrated mixture of 1a, monoimine 3a.H (+), and 2a.2H (2+) under similar acidic hydrolytic conditions. The equilibrium between 1b, c and 2b, c.2H (2+) to control the position of the macrocycle could be successfully switched to either side by applying acidic hydrolytic or dehydrating conditions. Furthermore, the equilibrium was largely biased to [2]rotaxane 2b, c.2H (2+) under acidic hydrolytic conditions and could be reversed in favor of bis-imine 1b, c just by heating. This is a successful example of a molecular shuttle exhibiting entropy-driven translational isomerism with remarkable positional discrimination. An examination of thermodynamic parameters showed that imine-bond hydrolyses and the formation of hydrogen bonds between the macrocycle and the station are thermodynamically matched processes, because both processes are enthalpically favored and accompanied by a loss of entropy. The combination of imine-bonding and hydrogen-bonding station in a rotaxane system is the key to realizing the clear entropy-driven positional switching of the macrocycle observed.

A facile two-step synthesis of aza[7]helicenes possessing a 6-5-6-6-6-5-6 skeleton from commercially available 2,9-dichloro-1,10-phenanthroline via double amination with aniline derivatives followed by hypervalent iodine reagent-mediated intramolecular double-NH/CH couplings was developed. Single-crystal X-ray analyses of the helicenes revealed unique structures, including both a significantly twisted center and planar terminals of the skeleton. The azahelicenes show high fluorescent quantum yields (Φs) under both neutral (Φ: 0.25-0.55) and acidic conditions (Φ: up to 0.80). An enantiomerically pure aza[7]helicene showed high circularly polarized luminescence (CPL) activity under both neutral and acidic conditions (g : up to 0.009).

We have developed a two- or three-step synthesis of polyaza[5]–[9]helicenes by consecutive N–H/C–H coupling with a hypervalent iodine reagent.

Establishing methods to control submolecular movements of rotaxane components is a prerequisite for the development of artificial devices that function through translational and rotational motion at the molecular level. During the last decade, many systems capable of controlling interactions among components through external stimuli, such as metal binding, change in pH value, electrochemistry, light, or temperature, have been developed to realize on/off switching