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 (gabs = ca. 2 x 10–2). 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 gabs = ca. 10–1. 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.