scholarly journals Macroscopic chirality of twist-bend nematic phase in bent dimers confirmed by circular dichroism

2020 ◽  
Vol 8 (3) ◽  
pp. 1041-1047 ◽  
Author(s):  
Warren D. Stevenson ◽  
Xiangbing Zeng ◽  
Chris Welch ◽  
Anil K. Thakur ◽  
Goran Ungar ◽  
...  
Keyword(s):  
Circular Dichroism ◽  
Long Range ◽  
Nematic Phase ◽  
Polarized Light ◽  
Circular Dichroism Spectroscopy ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Left And Right ◽  
Circular Dichroïsm

Long-range global chirality is confirmed in the twist-bend nematic phase of bent dimers using circular dichroism spectroscopy. The phase absorbs left and right circularly polarized light differently, confirming its helical rather than wavy character.

Correction for Unequal Intensities of Left and Right Circularly Polarized Light in Steady-State and Lifetime-Resolved Fluorescence-Detected Circular Dichroism

1994 ◽  
Vol 48 (2) ◽  
pp. 167-175 ◽  
Author(s):  
Lei Geng ◽  
Linda B. McGown
Keyword(s):  
Circular Dichroism ◽  
Steady State ◽  
General Scheme ◽  
Multicomponent System ◽  
Polarized Light ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Experimental Approaches ◽  
Total Absorbance ◽  
Circular Dichroïsm

A major difficulty in fluorescence-detected circular dichroism (FDCD) and lifetime-resolved fluorescence-detected circular dichroism (LRFDCD) is the generation of equal excitation intensities of left circularly polarized light (LCPL) and right circularly polarized light (RCPL). In the presence of unequal intensities, the observed FDCD signal of an optically active sample, or the resolved FDCD signals of a multicomponent system in the case of LRFDCD, will be contaminated by a factor that is the ratio of the two unequal intensities. For optically inactive samples, a sample-independent, artifactual, nonzero signal of constant magnitude is observed. A general scheme is presented for the correction of these inaccuracies caused by unequal intensities of LCPL and RCPL. Large differences between LCPL and RCPL excitation intensities were artificially introduced in steady-state FDCD measurements, and the artifact was accurately corrected by the scheme. Corrected results for the different experimental approaches that have been described for LRFDCD showed similarly good accuracy. In a related consideration, inclusion of the total absorbance and absorption circular dichroism of the sample in the calculation of the FDCD signal is shown to be essential for samples with high absorbances.

Philip John Stephens. 9 October 1940 — 31 July 2012

2013 ◽  
Vol 59 ◽  
pp. 359-382 ◽  
Author(s):  
Andrew J. Thomson ◽  
Laurence D. Barron
Keyword(s):  
Circular Dichroism ◽  
Density Functional ◽  
Magnetic Circular Dichroism ◽  
Polarized Light ◽  
Deep Understanding ◽  
Chiral Drugs ◽  
Widespread Application ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Circular Dichroïsm

Philip J. Stephens was a theoretical chemist who brought to fruition two new forms of optical spectroscopy, using circularly polarized light, for the determination of electronic structure and molecular stereochemistry. The first was magnetic circular dichroism (MCD), the wavelength dependence of the differential absorption of left and right circularly polarized light induced by a magnetic field applied parallel to the light beam. Stephens established a methodology for extracting from MCD spectra the angular momentum characteristics of ground and excited electronic states and demonstrated applications to the assignment of the optical spectra of coordination complexes of transition metals and to metalloproteins. In the second half of his career Stephens led the field of vibrational circular dichroism (VCD), the measurement of the natural circular dichroism (CD) arising from the vibrational transitions of chiral molecules. He developed instrumental techniques to measure this weak dichroism over a wide frequency range with high sensitivity. Subsequently he developed a quantum-mechanical method that yielded reliable calculations of VCD spectra by using density functional theory. Thus absolute configurations of all the chiral centres in an organic molecule are readily established. Given the increasing importance of enantiomerically pure chiral drugs, VCD has found widespread application in the pharmaceutical industry. Philip had not only a deep understanding of chemical theory but also a thorough grasp of experiments. His lectures on theoretical topics were models of clarity. He was also an accomplished pianist in demand, when a student at Oxford University, as an accompanist and for chamber concerts.

scholarly journals Enhancement of Optical Chirality Using Metasurfaces for Enantiomer-Selective Molecular Sensing

2021 ◽  
Vol 11 (7) ◽  
pp. 2989
Author(s):  
Sangtae Jeon ◽  
Soo Jin Kim
Keyword(s):  
Circular Dichroism ◽  
Polarized Light ◽  
Physical Property ◽  
Circular Dichroism Spectroscopy ◽  
Molecular Structures ◽  
Circularly Polarized Light ◽  
Optical Resonances ◽  
Optical Chirality ◽  
Depth Analysis ◽  
Circular Dichroïsm

Circular dichroism (CD) is a physical property observed in chiral molecules by inducing the difference of absorption between left- and right-handed circularly polarized light (CPL). Circular dichroism spectroscopy is widely used in the field of chemistry and biology to distinguish the enantiomers, which typically show either positive or severe side effects in biological applications depending on the molecular structures’ chirality. To effectively detect the chirality of molecules, diverse designs of nanostructured platforms are proposed based on optical resonances that can enhance the optical chirality and amplify the signal of circular dichroism. However, the underlying physics between the optical chirality and the resonance in a nanostructure is largely unexplored, and thus designing rules for optimal chiral detection is still elusive. Here, we carry out an in-depth analysis of chiral enhancement (C enhancement) in nanostructured surfaces to find the relationship between optical resonances and chirality. Based on the relations, we optimize the nanostructured metasurface to induce effective chiral detection of enantiomers for diverse conditions of molecule distribution. We believe that the proposed designing rules and physics pave the important pathway to enhance the optical chirality for effective circular dichroism spectroscopy.

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