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 Pt^II 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.

Fig. 1. Monomer and polymer chemical structures and UV–vis studies.

Chemical structure of (a) mono-(S)-1 and mono-(S)-2. b Chemical structure of poly-(S)-1 and poly-(S)-2. c Comparison of experimental and theoretical UV–vis spectra of mono-(S)-1 and mono-(S)-2 in DCM and DMF. [mono-(R)-1] = 0.3 mg/mL, [mono-(R)-2] = 0.3 mg/mL. (Abs, absorbance).

Fig. 2. ECD studies of poly-(S)-1 in different solvents and main scaffolds adopted by poly(phenylacetylene)s.

a) UV-vis spectra of poly-(S)-1 in THF, DCM and DMF and poly-(S)-2 in DMF. b ECD spectra of poly-(S)-1 in THF and DCM. c ECD spectra of poly-(S)-1 and poly-(S)-2 in DMF. d Schematic representation of the helical structure of PPA in a cis-cisoidal and a cis-transoidal conformation. [poly-(R)−1] = 0.6 mg/mL, [poly-(R)−2] = 0.6 mg/mL. (Abs, absorbance; ECD, electronic circular dichroism).

Fig. 3. Theoretical ECD studies and approximated 3D structure for poly-(S)-1.

a Representation of the calculated models for the assembly of three units of mono-(S)-1 in a left-handed and a right-handed helix with the calculated ECD spectra. b Illustration and ECD of the 3D model of a c-c helix of poly-(S)-1 resulting in a multihelical material composed of 5 helices. [poly-(R)-1] = 0.6 mg/mL. (ECD, electronic circular dichroism).