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Circular Dichroism and Linear Dichroism

Electronic Absorption and Luminescence

  1. Alison Rodger

Published Online: 15 SEP 2006

DOI: 10.1002/9780470027318.a5402

Encyclopedia of Analytical Chemistry

Encyclopedia of Analytical Chemistry

How to Cite

Rodger, A. 2006. Circular Dichroism and Linear Dichroism. Encyclopedia of Analytical Chemistry. .

Author Information

  1. University of Warwick, Coventry, UK

Publication History

  1. Published Online: 15 SEP 2006

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Abstract

Circular dichroism (CD) is the difference in absorption, A, of left and right circularly polarized light, Equation (1):

  • equation image(1)

For randomly oriented systems such as solutions of molecules, only chiral molecules will show any CD intensity corresponding to their absorption bands. Chiral molecules are those molecules that cannot be superposed on their mirror images.1 Chiral is derived from the Greek word χɛιρ meaning hand, hence the alternate term for chirality, “handedness”. Two molecules that are mirror images of each other are often referred to as enantiomers and equimolar mixtures of two enatiomers form a racemic mixture which has no net CD intensity in solution.

Linear dichroism (LD) is the difference in absorption of light linearly polarized parallel and perpendicular to an orientation axis, Equation (68):

  • equation image(68)