Multiple-Helical π-Conjugated Polymers
Biopolymers typically exhibit dynamic folding into complex hierarchical structures. We prepared the first π-conjugated polymer that exhibited a multiple-helical “quaternary structure” of polymer chains that underwent partially reversible unfolding and refolding. Key Publications. Nano Lett. 2008, Adv. Mater. 2008, Angew. Chem. 2006. Further publications. Chem. Eur. J. 2009, Chem. Eur. J. 2008, Macromol. Rapid Commun. 2008, Macromol. Biosci,. 2007.
State of the Research
Biopolymers attain complex hierarchical structures by dynamically folding the polymer chains into segments (secondary structure), arranging the latter in space (tertiary structure), and subsequent intermolecular aggregation (quaternary structure). Synthetic polymers that mimic this folding have been prepared by the “foldamer approach” (Moore, Chem. Rev. 2001, 101, 3893), but higher order structures have rarely been obtained in this way. Oligopeptides and oligopeptide-modified polymers exhibit a well-understood formation of nanostructures (Boden, Proc Natl. Acad. Sci. 2001, 98, 11857). Using those supramolecular scaffolds for polymerization reactions had previously not been reported.
We prepared molecules that comprised a polymerizable diacetylene unit, an oligopeptide segment, as well as a terminally attached hydrophobic, flexible, and amorphous polymer segment. Aggregation of the chiral oligopeptides by intermolecular N–H···O=C hydrogen bond formation furnished tape-like one-dimensional aggregates that displayed supramolecular helicity. The helical twisting combined with the steric demand of the attached polymer segments limited lateral aggregation. This resulted in the formation of uniform nanofibrils with a length of many micrometers. Subsequent polymerization of the diacetylene units within each tape then furnished the first example of a π-conjugated polymer with a complex “quaternary structure” of entwined multiple-helical polymer chains and partially reversible unfolding (Nano Lett. 2008, Adv. Mater. 2008, Angew. Chem. Int. Ed. 2006), similar to what is observed in biopolymers.