Helical dendronized polyphenylacetylenes
Electroactive donor or acceptor polymers jacketed by complimentary acceptor or donor self-assembling dendrons self-organize into two-dimensional lattices of nanowires. The columnar assemblies (i.e., the wires) possess internal helical order. We envision that columnar structures with single-handed helical order will improve the already high charge carrier mobility. Herein we explore opportunities to exploit polyphenylacetylene as the linear polymer backbone in combination with self-assembling dendrons, which are composed of benzyl ether dendrons appended with an aliphatic periphery. Cis-transoidal polyphenylacetylene adopts a helical conformation in solution and the helix sense can be selected by incorporation of chiral, non-racemic side chains. 6πElectrocyclization of 1,3- cis,5-hexatriene sequences creates cyclohexadiene repeat units. Chain cleavage occurs from extrusion of triphenylbenzene due to rearomatization of cyclohexadiene repeat units. The decrease of molecular weight is accelerated due to an apparent photosensitized oxidation of the polyene backbone. Because the Cotton effect observed by circular dichroism spectroscopy decreases due to cyclization, variable temperature experiments incorrectly probe helix dynamics. A library of dendritic phenylacetylene macromonomers was prepared and polymerized using a Rh(I)-based catalyst. Microphase segregation of the two regions generates cylindrical macromolecules that self-organize into nematic or various hexagonal columnar lattices. One dendron architecture provided a match to the pitch of the helical polyphenylacetylene backbone. Incorporation of chiral, non-racemic aliphatic periphery selects a particular handedness of the helix. The backbone undergoes an unprecedented cis-cisoidal-to- cis-transoidal isomerization at elevated temperatures. In the cis-transoidal conformation, cyclization cannot take place.
Rudick, Jonathan Gallagher, "Helical dendronized polyphenylacetylenes" (2005). Dissertations available from ProQuest. AAI3197734.