SYNTHESIS OF HELICAL CONJUGATED LADDER POLYMERS

The synthesis is described of the first helical ladder polymers with u nbroken pathways of conjugation that extend not only through each mono meric unit, but between them as well. The key step is the condensation of 1,2-phenylenediamine and a transition metal salt with a helicene h aving salicylaldehyde's functionality at both ends. This gives rise to ''metal salophen'' units that bind adjacent helicenes, provide conjug ated links from one ring system to the next, and constrain the p-orbit als of the rings they unite to be nearly parallel. Because the helicen e monomers are enantiopure, so too are the polymeric structures to whi ch they give rise. One of the polymers (6) winds continuously in only one direction. Another (4a) winds in one direction through the helicen e moieties and in the other direction through the metal-salophens. The circular dichroisms of the former at wavelengths near 600 nm are nota bly large. The corresponding circular dichroisms of the latter are muc h smaller. MALDI-TOF mass spectra provide particularly strong evidence for the structures assigned. The polymers are very soluble in a varie ty of organic solvents and seem to have number average molecular weigh ts of ca. 7000.