Coaxial Helices in Chiral Supramolecular Aggregates from Highly Hindered Chiral Allenes.

Chiral allenes self-assembly following a cooperative mechanism into a supramolecular chiral aggregate consisting of two coaxial helices: the internal helix described by the allene stack and the external helix which consist in a 4-helix described by the four allene substituents. More precisely, this supramolecular aggregate possesses six axially chiral elements within its structure-the allene, the allene stack (internal helix) and the stacks of the four allene substituents (external 4-helix)-. Interestingly, slight variations in the magnitude of the tilting degree while keeping its P- or M- orientation (internal helix) can vary the orientation of the 4-axial motifs at the external helix.

Macromolecular Switch Based on Conformational Control Exerted by an Achiral Side Chain within an Axially Chiral Locked Pendant.

Molecular switches, supramolecular chemistry, and polymers can be combined to create stimuli-responsive multichiral materials. Therefore, by acting on the extended/bent conformational composition of an achiral arm, it is possible to create a macromolecular gear, where different supramolecular interactions can be activated/deactivated to control the helical sense of a polymer containing up to five different chiral axial motifs. For this, a chiral allene with a flexible achiral arm was introduced as a pendant in poly(phenylacetylene).

Stimuli-responsive synthetic helical polymers.

Synthetic dynamic helical polymers (supramolecular and covalent) and foldamers share the helix as a structural motif. Although the materials are different, these systems also share many structural properties, such as helix induction or conformational communication mechanisms. The introduction of stimuli responsive building blocks or monomer repeating units in these materials triggers conformational or structural changes, due to the presence/absence of the external stimulus, which are transmitted to the helix resulting in different effects, such as assymetry amplification, helix inversion or even changes in the helical scaffold (elongation, J/H helical aggregates).

Dynamic Axial-to-Helical Communication Mechanism in Poly[(allenylethynylenephenylene)acetylene]s under External Stimuli.

Helix inversion in chiral dynamic helical polymers is usually achieved by conformational changes at the pendant groups induced through external stimuli. Herein, a different mechanism of helix inversion in poly(phenylacetylene)s (PPAs) is presented, based on the activation/deactivation of supramolecular interactions. We prepared poly[(allenylethynylenephenylene)acetylene]s (PAEPAs) in which the pendant groups are conformationally locked chiral allenes.