Thomas Bjornholm (1), Witold Brostow (2), Kjeld Schaumburg (1), Peter V. Shibaev (1,3,*), Vladimir Sinani (4), Rostislav Vinokur (3)

(1) Centre for Interdisciplinary Studies of Molecular Interactions (CIMSI), University of Copenhagen, Fruebjergvej 3, DK-2100, Copenhagen Ø, Denmark 
(2) Laboratory of Polymers and Composites (LAPOM), Departments of Materials Science and Chemistry, University of North Texas, Denton, TX 76203-5310, USA; brostow@unt.edu 
(3) Department of Physical Electronics, Moscow State University, 119899 Moscow, Russia
(4) Department of Chemistry, Moscow State University, 119899 Moscow, Russia
(*) Author for correspondence at ps@symbion.ki.ku.dk

ABSTRACT

Chiral derivates of poly(3-(S-3',7'-dimethyloctyl)thiophene) embedded in either poly(methyl methecrylate) (PMMA) or poly(butyl methacrylate) (PBMA) were studied by polatization optical microscopy, UV absortion and circular dichroism (CD) spectroscopy as well as simulated using the Molecular Dynamics Procedure. CD spectra change on heating to mirror spectra; for PMMA-containing blends the changes in heating/cooling cycles are reversible. The signs of CD spectra depend on free volume, the packing of side groups in particular. Since in the melt there are no restrictions on the positions of the chiral groups, those groups appear with equal probabilities at any location with respect to the thiophene ring. By contrast, in clusters restrictions imposed by other alkyl chains result in positioning of chiral methyl groups preferencially on the left or right sides of the thiophene rings. The consequence is the formation of right or left twists in molecular backbones.