Multi-chiral materials comprising metallosupramolecular and covalent helical polymers containing five axial motifs within a helix

Abstract

Supramolecular and covalent polymers share multiple structural effects such as communication mechanisms among monomer repeating units, which are related to their axial helical structure. Herein, a unique multi-helical material combining information from both metallosupramolecular and covalent helical polymers is presented. In this system, the helical structure described by the poly(acetylene) (PA) backbone (cis-cisoidal, cis-transoidal) guides the pendant groups in a fashion where a tilting degree emerges between a pendant and the adjacent ones. As a result, a multi-chiral material is formed comprising four or five axial motifs when the polyene skeleton adopts either a cis-transoidal or cis-cisoidal configuration: the two coaxial helices—internal and external—and the two or three chiral axial motifs described by the bispyridyldichlorido PtII complex array. These results show that complex multi-chiral materials can be obtained by polymerizing appropriate monomers that combine both point chirality and the ability to generate chiral supramolecular assemblies.

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

“…Thus, the allene group not only functions as a helix inductor due to its intrinsic chirality, but creates a supramolecular array within the helical scaffold of the polymer, generating yet another chiral motif, previously observed only for nonchiral planar spacers as OPEs or bispyridyldichlorido Pt(II) complexes. 40,41 Consequently, five different axial motifs are found in a PAEPA: the allene, the internal helix, the external helix and two allene axial arrays (P allene , M int /P ext /P axial-1 /P axial-2 ) (Figure 5d). Finally, to further demonstrate that the dynamic behavior of poly-(P)-1 is due to variations in the conformational composition of side chain c containing the sulfonamide group, a titration with different anions such as N 3 − , CN − , and F − (introduced as tetrabutylammonium salts: TBAN 3 , TBACN, TBAF, 0.35 mM in MeCN) were added to 1,2-DCE solutions of poly-(P)-1 slowly cooled at 268 K whose side chain c adopted, consequently, a bent conformer (Figure 6 for TBAN 3 and Sections 16 and 17 of the Supporting Information for other salts).…”

“…Recently, our group reported that the use of rigid and planar spacers such as oligophenylenethynylenes (OPEs) or bispyridyldichlorido Pt­(II) complexes between the polyene backbone and the chiral pendant , can produce, in certain scaffolds, a new chiral axial arrangement of the spacers within the helical scaffold whose ECD pattern dominates the ECD spectra of the whole helical system. In these polymers, helix induction in the polyene backbone follows a chiral harvesting mechanism, where chiral information from the axial array of the spacer is harvested by the polyene backbone.…”

“…Thus, the allene group not only functions as a helix inductor due to its intrinsic chirality, but creates a supramolecular array within the helical scaffold of the polymer, generating yet another chiral motif, previously observed only for nonchiral planar spacers as OPEs or bispyridyldichlorido Pt­(II) complexes. , Consequently, five different axial motifs are found in a PAEPA: the allene, the internal helix, the external helix and two allene axial arrays ( P allene , M int / P ext / P axial‑1 / P axial‑2 ) (Figure d).…”

“…Dynamic helical polymers are macromolecular switches − where the P/M screw sense control is achieved by resorting to different helix induction mechanisms that arise from the conformational manipulation of the pendant of a monomer repeating unit because of interactions with different stimuli. Thus, information from the chiral center to the main chain of the polymer can be transmitted directly, across space, through helical induction effects such as tele-induction, − chiral overpass, , or substituent overpass, or indirectly, in a two-step process, where information from a chiral group placed at a remote position on the pendant is first transmitted to an achiral spacer and then harvested by the polyene backbone (chiral harvesting). − In copolymers, Zentel et al designed an isocyanate copolymer that shows reversible helix-inversion induced by isomerization of an azobenzene group. , …”