A light-operated pillar[6]arene-based molecular shuttle.

A molecular shuttle comprising a pillar[6]arene macrocyclic ring and an axle with two equal-energy-level stations connected by an azobenzene unit was synthesised. The E isomer of the azobenzene functioned as "open gate", allowing the pillar[6]arene ring to rapidly shuttle back-and-forth between the two stations. Ultraviolet irradiation induced photo-isomerisation of the azobenzene from E to Z form.

Spacer Length-Independent Shuttling of the Pillar[5]arene Ring in Neutral [2]Rotaxanes.

For a series of neutral [2]rotaxanes consisting of a pillar[5]arene ring and axles possessing two stations separated by flexible spacers of different lengths, the free energies of activation for the ring shuttling between the stations were found to be independent of the spacer length. The constitution of the spacer affects the activation energies: replacement of CH groups by repulsive oxygen atoms in the axle increases the barrier. The explanation for the observed length-independence lies in the presence of a barrier for re-forming the stable co-conformation, which makes the ring travel back and forth along the thread in an intermediate state.

Synthesis of a pillar[5]arene-based [2]rotaxane with two equivalent stations via copper(I)-catalyzed alkyne-azide cycloaddition.

A one-pot synthesis of pillar[5]arene-based [2]rotaxanes containing one and two stations by copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction is reported. In situ formation of the two stations by two stepwise CuAAC reactions allows for the synthesis of a [2]rotaxane containing two stations with equal energy levels that exhibit shuttling of the pillar[5]arene wheel.

Clickable di- and tetrafunctionalized pillar[n]arenes (n = 5, 6) by oxidation-reduction of pillar[n]arene units.

We report a new route for the selective synthesis of di- and tetrafunctionalized pillararenes via oxidation and reduction of the pillararene units. Hypervalent-iodine oxidation of perethylated pillar[5]arene afforded pillar[5]arene derivatives containing one benzoquinone unit and two benzoquinones at the A,B- and A,C-units. A pillar[6]arene derivative containing one benzoquinone unit was also synthesized.