Percec Virgil, Peterca Mihai, Rudick Jonathan G, Aqad Emad, Imam Mohammad R, Heiney Paul A
Roy & Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA.
Chemistry. 2007;13(34):9572-81. doi: 10.1002/chem.200701008.
The first example of a self-assembling phenylpropyl ether based dendronized polymer has been reported and its preferred helical handedness has been determined. Dendronized polymer poly(10) and its nondendritic analogue poly(8) are high-cis-content polyphenylacetylenes (PPAs) prepared by using [Rh(nbd)Cl]2/NEt3 (nbd: 2,5-norbornadiene). Both polymers possess a stereocenter in their side chain, which selects a preferred helical handedness. Based on negative exciton chirality observed in the CD spectra of poly(10), we have designated this molecule as a right-handed helical polymer, which persists over a wide temperature range. Poly(10) self-organizes into both Phiioh and Phih lattices in bulk. The Phiioh-to-Phih transition is associated with thermoreversible cis-cisoidal to cis-transoidal isomerization of the helical PPA, accompanied by a dramatic decrease in the column diameter and a decrease in the pi-stacking correlation length along the column. A model for the right-handed helical dendronized PPA has been proposed wherein dendrons from adjacent column strata interdigitate to effectively fill space.
