title: Circular dichroism imaging microscopy: application to enantiomorphous twinning in biaxial crystals of 1,8-dihydroxyanthraquinone.
abstract: A microscope was constructed for imaging circular dichroism of heterogeneous anisotropic media. To avoid linear biases that are common with electronic circular polarization modulation, we chose a retrogressive solution: mechanical light modulation by rotating a linear polarizer with respect to a quarter wave plate continuously tuned by tilting to the operating wavelength. Our comparatively slow technique succeeds with near-perfect circular input and signal averaging using a CCD camera. We have applied the method to anomalously birefringent crystals of 1,8-dihydroxyanthraquinone that are shown to have intergrown mirror image domains, undetected by X-ray diffraction because the twinning complexity renders differences in anomalous dispersion, already small, unreliable. The origin of the anomalous birefringence and the assignment of the absolute configuration are discussed.
authors.affiliation: Department of Chemistry, Box 351700, University of Washington, Seattle, WA 98195-1700, USA.
authors.forename: Kacey
authors.initials: K
authors.lastname: Claborn
authors.forename: Eileen
authors.initials: E
authors.lastname: Puklin-Faucher
authors.forename: Miki
authors.initials: M
authors.lastname: Kurimoto
authors.forename: Werner
authors.initials: W
authors.lastname: Kaminsky
authors.forename: Bart
authors.initials: B
authors.lastname: Kahr