Molecular Meccano, Part 44 [ = ] Photoactive Azobenzene-Containing Supramolecular Complexes and Related Interlocked Molecular Compounds Masumi Asakawa, [b] Peter R. Ashton, [b] Vincenzo Balzani,* [a] Christopher L. Brown, [b] Alberto Credi, [a] Owen A. Matthews, [b] Simon P. Newton, [b] Françisco M. Raymo, [b] Andrew N. Shipway, [b] Neil Spencer, [b] Andrew Quick, [c] J. Fraser Stoddart,* [b] Andrew J. P. White, [c] and David J. Williams* [c] Abstract: Two acyclic and three macro- cyclic polyethers, three [2]catenanes, and one [2]rotaxane, each containing one 4,4'-azobiphenoxy unit, have been synthesized. In solution, the azoben- zene-based acyclic polyethers are bound by cyclobis(paraquat-p-phenylene)Ða tetracationic cyclophaneÐin their trans forms only. On irradiation (l  360 nm) of an equimolar solution of the tetracat- ionic cyclophane host and one of the guests containing a trans-4,4'-azobiphe- noxy unit, the trans double bond isomer- izes to its cis form and the supramolec- ular complex dissociates into its molec- ular components. The trans isomer of the guest and, as a result, the complex are reformed, either by irradiation (l  440 nm) or by warming the solution in the dark. Variable temperature 1 H NMR spectroscopic investigations of the [2]ca- tenanes and the [2]rotaxane revealed that, in all cases, the 4,4'-azobiphenoxy unit resides preferentially alongside the cavities of their tetracationic cyclophane components, which are occupied either by a 1,4-dioxybenzene or by a 1,5-di- oxynaphthalene unit. In the acyclic and macrocyclic polyethers containing 1,4- dioxybenzene or 1,5-dioxynaphthalene chromophoric groups and a 4,4'-azobi- phenoxy moiety, the fluorescence of the former units is quenched by the latter. Fluorescence quenching is accompanied by photosensitization of the isomeriza- tion. The rate of the energy-transfer process is different for trans and cis isomers. In the [2]rotaxane and the [2]catenanes, the photoisomerization is quenched to an extent that depends on the specific structure of the compound. Only in one of the three [2]catenanes and in the [2]rotaxane was an efficient photoisomerization (l  360 nm) from the trans to the cis isomer of the 4,4'- azobiphenoxy unit observed. Single crystal X-ray structural analysis of one of the [2]catenanes showed that, in the solid state, the 4,4'-azobiphenoxy unit in the macrocyclic polyether component also resides exclusively alongside. The cavity of the tetracationic cyclophane component of the [2]catenane is filled by a 1,5-dioxynaphthalene unit, and infinite donor ± acceptor stacks between adja- cent [2]catenanes are formed in the crystal. These supramolecular com- plexes and their mechanically inter- locked molecular counterparts can be regarded as potential photoactive nano- scale devices. Keywords: catenanes ´ molecular devices ´ molecular recognition ´ rotaxanes ´ template synthesis [a] Prof. V. Balzani, Dr A. Credi Dipartimento di Chimica G. Ciamician, Universita Á di Bologna Via Selmi 2, I-40126 Bologna, Italy Fax: ( 390) 51-259456 E-mail: vbalzani@ciam.unibo.it [b] Prof. J. F. Stoddart, [] Dr M. Asakawa, Dr C. L. Brown, Dr O. A. Matthews, Dr S. P. Newton, Dr F. M. Raymo, [] Dr A. N. Shipway, Dr N. Spencer, P. R. Ashton School of Chemistry, University of Birmingham Edgbaston, Birmingham, B15 2TT (UK) [c] Prof. D.J. Williams, Dr A. Quick, Dr A. J. P. White Department of Chemistry, Imperial College South Kensington, London, SW7 2AY (UK) Fax: ( 44) 171-594-5835 [] Current address: Department of Chemistry and Biochemistry, University of California Los Angeles, 405 Hilgard Avenue, Los Angeles CA 90095-1569 (USA) Fax: ( 1) 310-206-1843 E-mail: stoddart@chem.ucla.edu [ = ] Part 43: P. R. Ashton, M. C. T. Fyfe, S. K. Hickingbottom, J. F. Stod- dart, A. J. P. White, D. J. Williams, J. Chem. Soc. Perkin Trans. 2 1998, 2117 ± 2128. FULL PAPER  WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999 0947-6539/99/0503-0860 $ 17.50+.50/0 Chem. Eur. J. 1999, 5, No. 3 860