Form dichroism and the study of molecular shape

Journal article, 1978

Form dichroism is the absorptive analogue of form birefringence and can be observed in anisotropic media which have complex permittivity. Two theoretical treatments of form dichroism are presented: first, for a uniaxial crystal using a simple polariton formalism, secondly for a solution of partially oriented ellipsoidal molecules by using an earlier flow birefringence model. The two descriptions can be made equivalent by introducing relative permittivities, which takes into account the medium surrounding the molecules in the crystal, and by defining the crystal anisotropy so that it describes the shape of the material distribution. The results show that form dichroism provides a method for determining the shape of macromolecules that are built up of isotropic or isotropically oriented chromophoric units. Compact DNA and detergent micelles are discussed as examples.