Mechanically Interlaced and Interlocked Donor-Acceptor Foldamers

The emergence of a class of organic oligomers and polymers that lie at the intersection of the fields of mechanically interlocked molecules (MIMs) and synthetic foldamers is described in this review. These macromolecules are based on 4,4'-bipyridinium (BIPY2+) and 1,5-dioxynaphthalene (DNP) recognition units incorporated into linear oligo- or polymeric chains (threads) and macrocycles (rings), where the threads fold their way through a series of rings in a serpentine-like fashion. The well-defined geometries of these polyelectrolytes are rendered by the [C-H center dot center dot center dot O] hydrogen bonding interactions that transpire between the polyether chains appended to DNP and the acidic protons of BIPY2+, as well as the pi-pi and donor-acceptor (D-A) charge transfer interactions that cause DNP and BIPY2+ units to pack into extended mixed stacks. The unique folding motif of these pseudorotaxanes and rotaxanes makes them attractive candidates for novel multiferroic and mechanically tunable materials.