The Competitive Aggregation Pathway of an Asymmetric Chiral Oligo(<i>p</i>‐phenyleneethynylene) Towards the Formation of Individual <i>P</i> and <i>M</i> Supramolecular Helical Polymers
Zulema Fernández, Berta Fernández, Emilio Quiñoá, Félix Freire
Abstract
Abstract A complex aggregation pathway towards two diastereomeric P and M supramolecular helices arises from the aggregation of a short, chiral, and rigid oligo(phenyleneethynylene) [OPE, ( S )‐ 1 ]. Thus, while Agg I aggregate is obtained when a DCM solution of ( S )‐ 1 is diluted with MCH at room temperature, Agg II aggregate is generated only after a slow heating (353 K)/cooling (273 K) process. Interestingly, during Agg I formation (mechanism 1), short P chain oligomers are produced, which have a great tendency to aggregate in plane, yielding brick‐like nanostructures that halt the aggregation process. On the other hand, after a heating/cooling cycle, long M type columnar helical aggregates ( Agg II ) are obtained, formed by individual supramolecular polymer chains (mechanism 2) easily visualized by AFM. The two different P / M orientations obtained for Agg I and Agg II reveal the dynamic character of the system and its ability to create diastereomeric helical structures under the right conditions. Different experimental protocols were explored to prepare long M type columnar helical aggregates, which are not obtained by using the previous MCH/DCM 99/1 (v/v) solvent mixture. The generation of the desired M oriented supramolecular polymer is achieved when toluene is added to the solvent mixture in a 97/2/1 MCH/Tol/DCM (v/v/v) ratio.