Optical activity poly chiral aggregates

Poly (PDBF) s synthesized by helix-sense-selective polymerization using FlLi-Sp and FlLi-DDB complexes did not show detectable CD or optical activity in solution. However, a thin film made by drop-casting the solution onto a quartz plate indicated intense CD absorptions. The spectra of the polymers synthesized with (+)- and (-)-DDB were almost mirror images. The CD spectra are not due to film anisotropy but to conformational chirality of polymer chains. Because the polymers showing clear CD bands in film did not show chiroptical properties in solution, molecular aggregation may amplify and stabilize the single-handed helical conformation induced... 

We have rationalized the optical activity of these PAn.HCSA (and related PAn.tartrate) salts in terms of the preferential adoption of a one-handed helical conformation by the PAn chains, depending on which enantiomer of the CSA anion is employed in the doping. - - Alternatively, as suggested by Meijer et al. ° (and has been established for chiral poly(alkylthiophenes) — see Chapter 6), the observed optical activity may arise from the formation of chiral supramolecular aggregates. However, in contrast to chiral poly(alkylthiopenes), PAn(+)- HCSA exhibits strong CD spectra in "good"... 

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