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

• Published in: Chemistry : a European journal 2024-06, Vol.30 (35), p.e202400706-n/a
• Main Authors: Tanaka, Rikuya, Yamaoka, Seiha, Ikeda, Shuichi, Okano, Kentaro, Horie, Masaki, Minami, Hideto, Suzuki, Nozomu, Mori, Atsunori
• Format: Article
• Language: English
• Subjects: aggregation; Aromatic compounds; Catalysts; chiral side chain; Chirality; Circular dichroism; Degree of polymerization; Dichloroethane; Dichroism; helix; Nickel; poly(1,4-phenylene); Solvents
• ISSN: 0947-6539; 1521-3765; 1521-3765
• DOI: 10.1002/chem.202400706

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. 2×10−2). 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. The use of nickel‐Chiraphos complex as a catalyst enables the synthesis of a variety of poly(1,4‐phenylene) with a chiral side chain and provides new insights into the correlation with their helical structure through the measurement of CD spectra.