Temperature-dependent chirality of cholesteric liquid crystal for terahertz waves

Chiral Lanthanum Metal-Organic Framework with Gated CO2 Sorption and Concerted Framework Flexibility

A metal–organic framework (MOF) CTH-17 based on lanthanum(III) and the conformationally chiral linker 1,2,3,4,5,6-hexakis(4-carboxyphenyl)benzene, cpb^6–: [La₂(cpb)]·1.5dmf was prepared by the solvothermal method in dimethylformamide (dmf) and characterized by variable-temperature X-ray powder diffraction (VTPXRD), variable-temperature X-ray single-crystal diffraction (SCXRD), and thermogravimetric analysis (TGA). CTH-17 is a rod-MOF with new topology och. It has high-temperature stability with Sohncke space groups P6₁22/P6₅22 at 90 K and P622 at 300 and 500 K, all phases characterized with SCXRD and at 293 K also with three-dimensional (3D) electron diffraction. VTPXRD indicates a third phase appearing after 620 K and stable up to 770 K. Gas sorption isotherms with N₂ indicate a modest surface area of 231 m² g^–1 for CTH-17, roughly in agreement with the crystal structure. Carbon dioxide sorption reveals a gate-opening effect of CTH-17 where the structure opens up when the loading of CO₂ reaches approximately ∼0.45 mmol g^–1 or 1 molecule per unit cell. Based on the SCXRD data, this is interpreted as flexibility based on the concerted movements of the propeller-like hexatopic cpb linkers, the movement intramolecularly transmitted by the π–π stacking of the cpb linkers and helped by the fluidity of the LaO₆ coordination sphere. This was corroborated by density functional theory (DFT) calculations yielding the chiral phase (P622) as the energy minimum and a completely racemic phase (P6/mmm), with symmetric cpb linkers representing a saddle point in a racemization process.

Review of optical sensing and manipulation of chiral molecules and nanostructures with the focus on plasmonic enhancements [Invited]

Chiral molecules are ubiquitous in nature; many important synthetic chemicals and drugs are chiral. Detecting chiral molecules and separating the enantiomers is difficult because their physiochemical properties can be very similar. Here we review the optical approaches that are emerging for detecting and manipulating chiral molecules and chiral nanostructures. Our review focuses on the methods that have used plasmonics to enhance the chiroptical response. We also review the fabrication and assembly of (dynamic) chiral plasmonic nanosystems in this context.

Microfluid-based soft metasurface for tunable optical activity in THz wave

Metasurfaces are usually planar structures and do not possess intrinsic chirality and therefore hardly generate optical activity. Here we realized a tunable optical activity in a terahertz wave through a microfluid-based soft metasurface. The meta-atom is a chiral structured microchannel made of soft polydimethylsiloxane and injected with the liquid metal Galinstan. A microfluid pressure system is bonded to the metasurface to reconfigure all meta-atoms simultaneously. By pumping glycerol liquid into the pressure system, the metasurface is deformed from a planar structure to a three dimensional one, which manifests intrinsic chirality for optical activity realization. By controlling the injected glycerol volume, a polarization rotation from 0°to 14° at 0.19 THz is demonstrated. The soft metasurface with tunable optical activity can be flexibly applied in various applications such as polarization microscopy, bio-detection and material analysis, etc.