High-Intensity Circular Dichroism of Head-To-Tail Regioregular Poly(1,4-Phenylene)s in the Aggregated State.

Circular dichroism (CD) studies on poly(1,4-phenylene)s bearing a chiral side chain in the aggregated conditions were carried out. Little CD was observed in a solution form, while addition of a poor solvent into the polyphenylene solution induced aggregation and a strong CD was observed, accordingly. Applying the controlled degree of polymerization (DP) of poly(1,4-phenylene) in the use of bidentate diphosphine Chiraphos as a ligand for the nickel catalyst, the relationship of DP with CD strength was studied to reveal to show the highest CD at the DP=84 (g=ca. 2×10). It was also found that the related aggregation was observed in good solvent 1,2-dichloroethane upon standing the solution at 4 °C for 3-23 days to observe g=ca. 10. Studies on the substituent effect of poly(1,4-phenylene) suggested that CD behaviors were dependent on the type of non-chiral substituent on the aromatic ring as well as the side-chain chirality.