RESUMO
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 AggI aggregate is obtained when a DCM solution of (S)-1 is diluted with MCH at room temperature, AggII aggregate is generated only after a slow heating (353â K)/cooling (273â K) process. Interestingly, during AggI 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 (AggII ) are obtained, formed by individual supramolecular polymer chains (mechanism 2) easily visualized by AFM. The two different P/M orientations obtained for AggI and AggII 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.
RESUMO
The helical stereomutation in the kinetically controlled coassembly of the reported carbonyl-bridged triarylamines (CBTs) is described. The copolymerization of chiral CBTs (S)-1 or (R)-1 with achiral 2 in sergeants-and-soldiers (SaS) experiments results in a tunable helicity conditioned by the percentage of the chiral sergeant and by the cooling rate. The dissimilar inherent chirality of the extended monomeric (M) and intramolecularly H-bonded metastable (M*) species, as well as the different stability of the kinetic trap of the chiral CBTs (S)-1/(R)-1 and the achiral CBT 2, condition the chirality transfer and afford J-aggregates of inverse handedness.