Photoactive azobenzene-containing supramolecular complexes and related interlocked molecular compounds.

Two acyclic and three macrocyclic polyethers, three [2]catenanes, and one [ 2]rotaxane, each containing one 4,4'-azobiphenoxy unit, have been synthesiz ed. In solution, the azobenzene-based acyclic polyethers are bound by cyclo bis(paraquat-p-phenylene)-a tetracationic cyclophane-in their trans forms o nly. On irradiation (lambda = 360 nm) of an equimolar solution of the tetra cationic cyclophane host and one of the guests containing a trans-4,4'-azob iphenoxy unit, the trans double bond isomerizes to its cis form and the sup ramolecular complex dissociates into its molecular components. The trans is omer of the guest and, as a result, the complex are reformed, either by irr adiation (lambda = 440 nm) or by warming the solution in the dark. Variable temperature H-1 NMR spectroscopic investigations of the [2]catenanes and t he [2]rotaxane revealed that, in all cases, the 4,4'-azobiphenoxy unit resi des 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'-azob iphenoxy moiety, the fluorescence of the former units is quenched by the la tter. Fluorescence quenching is accompanied by photosensitization of the is omerization. The rate of the energy-transfer process is different for trans and cis isomers. In the [2]rotaxane and the [2]catenanes, the photoisomeri zation is quenched to an extent that depends on the specific structure of t he compound. Only in one of the three [2]catenanes and in the [2]rotaxane w as an efficient photoisomerization (lambda=360 nm) from the trans to the ci s isomer of the 4,4'-azobiphenoxy unit observed. Single crystal X-ray struc tural analysis of one of the [2]catenanes showed that, in the solid state, the 4,4'-azobiphenoxy unit in the macrocyclic polyether component also resi des exclusively alongside. The cavity of the tetracationic cyclophane compo nent of the [2]catenane is filled by a 1,5-dioxynaphthalene unit, and infin ite donor-acceptor stacks between adjacent [2]catenanes are formed in the c rystal. These supramolecular complexes and their mechanically interlocked m olecular counterparts can be regarded as potential photoactive nanoscale de vices.