Rotaxanes with chiral stoppers and photoresponsive central unit

Two new chiral and photoisomerizable rotaxanes (9m, 9p) have been prepared, beating the longest non-polymeric axle known so far: the axles (6m, 6p) are polyether chains made of alternating triethyleneglycol/hydroquinone units, bearing a central meta- or para-azobenzoyl moiety and terminal tetraacetylglucoside stopper groups, while the wheel is the cyclobis(p- xylylene)bis(4,4'-bipyridinium) salt. Temperature dependent ¹H NMR measurements reveal that the translational process of the wheel across the azobenzene unit in the E-configuration is favoured for the para-rotaxane 9p compared to the meta isomer 9m. The azobenzene core of the free axles (6m, 6p) and rotaxanes (9m, 9p) undergo photochemical E/Z-isomerisation: from (E) to (Z) by irradiation at low wavelength and back from (Z) to (E) at high wavelength. Complete (Z) to (E) conversion was achieved by thermal isomerization.