Interchain Helically π-Stacked Assembly of Cationic Chiral Poly(para-phenylene) Derivatives Enforced by Anionic π-Conjugated Molecules through Both Electrostatic and π-π Interactions

Herein, a novel approach for preparing ionic, helically pi-stacked polymer assemblies with high dissymmetry factors is presented. We synthesized cationic chiral poly(para-biphenylene) [PPP1] and poly(para-terphenylene) [PPP2] derivatives by introducing alkyl substituents containing both asymmetric centers and quaternary ammonium cations into the side chains of the polymers. We discovered that these polymers have an intrachain helical structure bearing one-handed twisted main chains in solution; however, there was only a slight preference for one twisted conformation over its opposite. Subsequently, by adding an anionic pi-conjugated molecule to the cationic polymers, we prepared polymer assemblies bearing an interchain helically pi-stacked structure between the polymers and the molecules. Additionally, we clarified that the anionic molecule functioned as the binding species that closed the cationic pi-conjugated polymers through both electrostatic and pi-pi interactions. Although the polymer assembly of PPP1 was dissociated upon thermal heating, the formation of the polymer assembly of PPP2 was even developed due to thermal treatment of the polymer chains. The helically pi-stacked polymer assembly showed circular dichroism in both absorption and luminescence, yielding high dissymmetry factors of 10(-2)-10(-1). This approach using cooperative intermolecular electrostatic and pi-pi interactions should be useful for preparing various types of electrically and chiroptically active polymer assemblies.