Chiral nanostructure in polymers under different deposition conditions observed using atomic force microscopy of monolayers: poly(phenylacetylene)s as a case study

Abstract

This is the peer reviewed version of the following article: Freire, F. Quiñoá, E.; Riguera, R.; "Chiral nanostructure in polymers under different deposition conditions observed using atomic force microscopy of monolayers: poly(phenylacetylene)s as a case study" Chemical Communications, 2017, 53, 481-492 PPAs by atomic-force microscopy (AFM) are presented, with special attention to the methods for the preparation of monolayers, and their consequences in the quality of the AFM images. Thus, monolayers formed by drop casting, spin coating followed by crystallization or annealing, Langmuir-Blodgett and Langmuir-Schaefer methods, onto highly oriented pyrolytic graphite (HOPG) or mica are described, together with the AFM images and the resulting helical structure obtained for different PPAs. Also, some conclusions are assessed both on the adequacy of the different techniques for the formation of monolayers and on the solid supports employed to elucidate the secondary structure of different PPAs.

Chiral gold–PPA nanocomposites with tunable helical sense and morphology

“…As organic component of the composite, we chose poly(phenylacetylene)s [25][26][27][28][29][30][31][32][33] (PPA)s PPAs bearing amino acid residues as substituents. This class polymers adopt helical structures where the P /M helix is stabilized by hydrogen bonds between neighboring pendants -n th and (n+2) th or n th and (n+3) th -which are arranged into a b-sheet like orientation.…”

Predicting the Helical Sense of Poly(phenylacetylene)s from their Electron Circular Dichroism Spectra

“…Experimental methods like electron circular dichroism (ECD), X‐ray diffraction (XRD), or atomic force microscopy (AFM) provide wide information on their structure, but do not completely determine the helical sense of these polymers, which are made by two coaxial helices, internal helix described by the polyene backbone and external helix described by the pendant groups . For instance, CD studies provide information about the presence of a helical structure in the polyenic chain, but not the actual helical sense.…”

“…Moreover, the two coaxial helices of a PPA can rotate either in the same or in opposite directions depending on the dihedral angle between conjugated double bonds (ω 1 ). Thus, while in cis‐cisoidal (c‐c) PPAs internal and external helices rotate in the same direction, in a cis‐transoidal (c‐t) polymer both helices rotate in opposite directions . As a result, the information gathered from AFM (sense of the external helix) may be compatible with the two opposite senses in the internal helix leaving the structure unsolved.…”

Stimuli‐Directed Colorimetric Interconversion of Helical Polymers Accompanied by a Tunable Self‐Assembly Process

“…Dynamic helical polymers, such as poly(phenylacetylene)s (PPAs), are very interesting macromolecules largely due to their stimuli‐responsive properties. Their helical sense and elongation can be manipulated by the action of external stimuli such as chiral additives, polarity changes or metal ions .…”