Circular Dichroism and Linear Dichroism

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