Films constituted by an achiral host polymer and an achiral guest chromophore, which exhibit intense chiral optical responses for both host and guest peaks in the infrared as well as in the UV-visible regions, have been obtained. Such films can have any thickness from the nanoscale up to the macroscopic scale. This unexpected chiral optical behavior is easily achieved by crystallization of a robust commercial stereoregular host polymer (syndiotactic polystyrene, s-PS) from the amorphous phase as induced by a nonracemic guest, followed by exchange of the nonracemic guest with the achiral guest, leading to the formation of polymer-host/chromophore-guest cocrystalline phases. This finding opens the possibility to achieve s-PS-based films with chiral optical response at selected wavelengths. It has been also found that the chiral optical cocrystalline phase of s-PS with azulene exhibits a monoclinic δ-clathrate form with equal proportions of left- and right-handed helices. This confirms that the observed chiral optical behavior arises by the nonracemic native morphology of the crystalline regions, which has been induced by the temporary nonracemic guest.
[Show abstract][Hide abstract] ABSTRACT: For an industrially relevant specialty polymer, poly(2,6-dimethyl-1,4-phenylene)oxide (PPO), for the first time, a crystalline structure is resolved. It is a co-crystalline structure of the polymer with a chiral guest molecule (α-pinene), exhibiting a 2/1 monomer-unit–guest molar ratio. The most relevant feature of this co-crystalline structure is its chirality. In fact, the unit cell includes all left- or right-handed polymer helices and (1S)-(−)- or (1R)-(+)-α-pinene guest molecules, respectively. The induction of non-racemic macromolecular helicity in the co-crystalline structure, clearly confirmed by VCD measurements, leads to amplification of chirality. Guest extraction procedures from the PPO–α-pinene co-crystalline form produce optically inactive nanoporous-crystalline modifications, which present high sorption ability toward organic compounds.
[Show abstract][Hide abstract] ABSTRACT: Three different co-crystalline phases of syndiotactic polystyrene (s-PS) with azobenzene have been prepared and structurally characterized. The triclinic δ-clathrate phase is characterized by a styrene-monomeric-unit/guest ratio (SU/G) equal to 8/1 while the δ-intercalate phase is characterized by SU/lG = 4/1. The orthorhombic ε-clathrate phase allows stacking of a variable number of guest molecules per monomer unit with SU/G ≥ 9/1. Isomerization reactions of the azobenzene guest molecules (both photo-induced trans → cis and spontaneous cis → trans) have been studied by UV–Visible and FTIR measurements. Repeated isomerization cycles produce progressive desorption from the polymer film of azobenzene molecules being simply dissolved in s-PS amorphous phases, while poorly affect the content of azobenzene molecules being guest of s-PS co-crystalline phases. Polarized FTIR spectra of axially oriented films indicate that isomerizations occur without expulsion of azobenzene guest molecules from the polymer co-crystalline phases. The whole set of data indicate that films exhibiting co-crystalline phases of azobenzene with s-PS are suitable for producing self-erasing photo-isomerization patterns with molecular size marks.
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