Conformational transformations in chiral polythiophene derivatives aggregated in polymethacrylate matrices: Experiments and molecular dynamics simulations

Chiral derivatives of poly(3-(S-3',7'-dimethyloctyl)thiophene) embedded in either poly(methyl methacrylate) (PMMA) or poly(butyl methacrylate) (PBMA) were studied by polarization optical microscopy, UV absorption and circular dichroism (CD) spectroscopy as well as simulated using the Molecular Dynam ics procedure. CD spectra change on heating to mirror spectra; for PMMA-con taining blends the changes in heating/cooling cycles are reversible. The si gns of CD spectra depend on free volume, the packing of side groups in part icular. Since in the melt there are no restrictions on the positions of the chiral groups, those groups appears with equal probabilities at any locati ons with respect to the thiophene ring. By contrast, in clusters restrictio ns imposed by other alkyl chains result in positioning of chiral methyl gro ups preferentially on the left or right sides of the thiophene rings. The c onsequence is the formation of right or left twists in molecular backbones.