Mapping the local ambidextrous chirality in thin films of NTB phase by circular dichroism spectra

Huanan Yu; Chris Welch; Georg H Mehl

doi:10.1016/j.saa.2024.125682

Mapping the local ambidextrous chirality in thin films of N_TB phase by circular dichroism spectra

Spectrochim Acta A Mol Biomol Spectrosc. 2024 Dec 27:330:125682. doi: 10.1016/j.saa.2024.125682. Online ahead of print.

Authors

Huanan Yu¹, Chris Welch², Georg H Mehl³

Affiliations

¹ School of Materials and Chemistry, China Jiliang University, Hangzhou 310018, China. Electronic address: huanan-yu@cjlu.edu.cn.
² Department of Chemistry, University of Hull, Hull HU6 7RX, UK.
³ Department of Chemistry, University of Hull, Hull HU6 7RX, UK. Electronic address: G.H.Mehl@hull.ac.uk.

PMID: 39740582
DOI: 10.1016/j.saa.2024.125682

Abstract

Circular dichroism mapping (CDM) method was introduced by utilizing the highly collimated light beam of synchrotron radiation (SR) available at Diamond Light Source B23 beamline for scanning the thin films of the N_TB phase. We apply SR-CDM to two achiral dimeric materials exhibiting the N_TB phase: symmetric DTC5C9 and dissymmetric DTC5C9CB. The SR-CDM measurements directly capture the chiral information in the local N_TB domains, providing the ultimate complement to the theoretical predictions of the helical structures: the spontaneous symmetry breaking in N_TB phase is ambidextrous. The macroscopic chirality of the N_TB phase is determined by the combination of doubly degenerate locally chiral domains in the illuminated area. Additionally, we investigate the temperature dependence, as well as the dynamic nature of the local chirality in the N_TB phase by in-situ SR-CDM, confirming a chiral conversion influenced by the state of enantiomeric aggregation and a progressive unwinding of the helical structure in left-handed domains as the crystallization temperature is approached.

Keywords: Ambidextrous; Circular dichroism mapping; Local N(TB) domains; Structural chirality; “Twist and Bend” nematic phase.