Intra‐ and intermolecular charge‐transfer interactions between terminal electron donor and acceptor attached to poly(γ‐benzyl‐L‐glutamate) in solution

Abstract

AbstractPoly(γ‐benzyl‐L‐glutamate) having a terminal dimethylaminoanilide group as an electron donor (D) and a terminal 3,5‐dinitrobenzoyl group as an electron acceptor (A) (A‐[Glu(OBzl)]n‐D) was synthesized by the N‐carboxyanhydride method. Polymer samples were fractionated by gel chromatography and their number‐average degrees of polymerization n were determined by the absorbances of the terminal chromophores. These polymers in chloroform and dimethylformamide solutions showed a charge‐transfer (CT) absorption band around 455 nm, and the fraction of the polymer forming the CT complex was evaluated as a function of the chain length. CT absorption for short chains (n = 5 ∼ 20) was attributed to intramolecular CT complex in which the A‐[Glu(OBzl)]n‐D chain takes cyclic conformations. An optimum chain length for the intramolecular CT was found to be n ≅ 10, where the [Glu(OBzl)]n chain may most easily bend back to form cyclic conformations. Stronger CT absorption observed for longer chains than n = 20 was shown to be intermolecular, and an intermolecular head‐to‐tail aggregation was found to be a cause of the strong CT interaction. All helical A‐[Glu(OBzl)]n‐D chains were found to form the head‐to‐tail dimers in chloroform solution.