Lamellar-twisting-induced circular dichroism of chromophore moieties in banded spherulites with evolution of homochirality

Abstract

Banded spherulites are formed by crystallization of a chiral polymer that is end-capped with chromophore. Induced circular dichroism (ICD) of the chromophore can be found in the crystallized chiral polymers, giving exclusive optical response of the ICD. The ICD signals are presumed to be driven by the lamellar twisting in the crystalline spherulites, and the exclusive optical activity is attributed to the chirality transfer from molecular level to macroscopic level. To verify the suggested mechanism, the sense of the lamellar twisting in the crystalline spherulite is determined using PLM for the comparison with the ICD signals of the chromophore in the electron circular dichroism spectrum. The conformational chirality of the chiral polymer is determined by the vibrational circular dichroism spectrum. On the basis of the chiroptical results, evolution of homochirality from helical polymer chains (conformational chirality) to lamellar twisting in the banded spherulite (hierachical chirality) is suggested. Supramolecular chirality: By evolution of homochirality from helical polymer chains (conformational chirality) to twisting lamellae (hierarchical chirality), banded spherulites with preferential handedness are formed by crystallization of chiral polymers end-capped with chromophore through cooperative intramolecular and intermolecular interactions, changing the chromophore moiety from "optically inactive" to "optically active". © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.