Synthesis of Helical Conjugated Ladder Polymers

Abstract

The synthesis is described of the first helical ladder polymers with unbroken pathways of conjugation that extend not only through each monomeric unit, but between them as well. The key step is the condensation of 1,2-phenylenediamine and a transition metal salt with a helicene having salicylaldehyde's functionality at both ends. This gives rise to “metal salophen” units that bind adjacent helicenes, provide conjugated links from one ring system to the next, and constrain the p-orbitals of the rings they unite to be nearly parallel. Because the helicene monomers are enantiopure, so too are the polymeric structures to which they give rise. One of the polymers (6) winds continuously in only one direction. Another (4a) winds in one direction through the helicene moieties and in the other direction through the metal−salophens. The circular dichroisms of the former at wavelengths near 600 nm are notably large. The corresponding circular dichroisms of the latter are much smaller. MALDI-TOF mass spectra provide ...