Electric Dichroism and Polymer Conformation. I. Theory of Optical Properties of Anisotropic Media, and Method of Measurement
Electric Dichroism and Polymer Conformation. I. Theory of Optical Properties of Anisotropic Media, and Method of Measurement
复制标题
电二色性和聚合物构象。
DOI：
10.1021/ma60023a001
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发表时间：
1971
期刊：
影响因子：
5.5
通讯作者：
H. Scheraga
中科院分区：
文献类型：
--
作者：
T. Troxell;H. Scheraga
The use of Mueller matrix algebra to analyze the optical properties of anisotropic media is discussed. It is shown that the treatment of collinear transmission in a general anisotropic medium can be simplified, since the contribution from the average absorption can be factored out of the Mueller matrix. The various anisotropic optical properties contribute to the rotation of the plane of the incident linearly polarized light, and these properties can be measured. The major contributions to the net rotation (for weak interaction of the anisotropic medium with the light beam) are the linear dichroism, the linear birefringence, and the change in optical rotatory dispersion upon application of an external field. Since these all de-pend differently on the angle,, between the major axis of the output elliptically polarized light and the direction of the external (electric) field, they can be separated and measured; for light propagating perpendicular to the axis of a uniaxial medium, the linear dichroism is much larger than the other two effects in the region of an absorption band. A sum rule is applicable to the total linear dichroism spectrum. On the basis of these considerations, a technique is developed for measuring electric di-chroism, in which the Cary Model 60 spectropolarimeter is used (together with a parallel-plate cell) to obtain thedependence of the rotation on, on the strength of a static external electric field, and on the wavelength of the incident light. This method is much more sensitive than a conventional direct measurement of the separate absorbances of two mutually perpendicularly polarized light beams. Representative data on several-helical poly (amino acids) indicatethat the rotation shows the ex-pected dependence on 9 and on field strength.Linear dichroism (the anisotropic absorption of linearly v polarized light) arises primarily from the interaction between the electric dipoletransition moment y0¡ of a molecule and the electric field E of the incident electromagnetic radiation. No linear dichroism (LD) is observed in an isotropic (or random.) distribution of molecules because the average value of the yoi’s is such that absorption is the same in all directions, regardless of the polarization of the incident radiation; in such a case, one acquires information only about! y0j. On the other hand, if the molecules are dis-tributed anisotropically, ie, if they have been forced to align preferentially in some direction, linear dichroism will be observed (with detection being possible even for less than
