Favourable combination of axial coordination and inclusion for effective chiral transfer from metal porphyrin to nematic liquid crystals

ABSTRACT

The nickel octasubstituted tetraporphyrinate (Ni-S(+)TPP) was studied as a dopant of nematic mixtures based on alkoxycyanobiphenyls (CB-6) and Schiff bases (SB-2). An analysis of the textures allowed to establish the formation of chiral nematic phases, to measure their clearance temperatures, the degree of dopants influence on the LC, and helical pitch. High helical twisting power was calculated (126.5 μm-1 for CB-6 and 63.5 μm-1 for SB-2). Anomalous temperature dependences of the LC dielectric permittivity were obtained, due to competition between the chiral dopant, which twisted the mesophase, and the magnetic field, which untwisted LC helix. On the base of quantum chemical calculations, the formation of stable solvates of Ni-S(+)TPP with 1 and 2 alkoxycyanobiphenyl molecules due to axial coordination and inclusion was established. Solvates involving Schiff bases are less stable due to the impossibility of axial coordination. These conclusions were confirmed by ¹H NMR and ROESY.

Graphical abstract

KEYWORDS:

• Chiral nematic phases
• dopant
• helical twisting power
• NMR spectroscopy
• nickel porphyrinate

Acknowledgments

Given study was supported by the Russian Foundation for Basic Research (Grant N18-03-00498). Quantum chemical calculations were carried out as a part of State Task of the Ministry of Science and Higher Education of the Russian Federation № FZZW-2020-0008.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This work was supported by  Russian Foundation for Basic Research [Grant N18-03-00498] and State Task of the Ministry of Science and Higher Education of the Russian Federation [№ FZZW-2020-0008].