Rotaxanes with Chiral Stoppers and Photoresponsive Central Unit

Christopher Kauffmann; Walter M. Müller; Fritz Vögtle; Sarah Weinman; Sarah Abramson; Benzion Fuchs

doi:10.1055/s-1999-3466

Synthesis 1999; 1999(5): 849-853
DOI: 10.1055/s-1999-3466

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Rotaxanes with Chiral Stoppers and Photoresponsive Central Unit

Christopher Kauffmann^* , Walter M. Müller, Fritz Vögtle, Sarah Weinman, Sarah Abramson, Benzion Fuchs

^*Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany; Fax +49(2 28)73 56 62; E-mail: voegtle@uni-bonn.de

Abstract

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Two new chiral and photoisomerizable rotaxanes (9m, 9p) have been prepared, bearing 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.

rotaxane - azobenzene isomerization - molecular recognition - chirality - supramolecular chemistry

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