Imaging chiroptical artifacts

Abstract

It is well-known that circular dichroism (CD) measurements of anisotropic media may contain artifacts that result from mixed linear anisotropies. Such artifacts are generally considered a nuisance. However, systematic artifacts, carefully measured, may contain valuable information. Herein, polycrystalline spherulites of D-sorbitol grown from the melt were analyzed with a Mueller matrix microscope, among other differential polarization images devices. As spherulites grew into one another they developed strong apparent optical rotation and CD signals at the boundaries between spherulites. These signals are shown not to have a chiroptical origin but rather result from the interactions of linear anisotropies in polycrystalline bodies. Such chiroptical artifacts should not be dismissed reflexively. Rather, they are comprehensible crystal-optical effects that serve to define mesoscale structure.

Enantioselective control of lattice and shape chirality in inorganic nanostructures using chiral biomolecules

“…On a fundamental level, these systems are expected to be intriguing candidates for studies of mechanisms acting in chiral crystallization, as well as studies of binding of organic molecules to chiral surfaces 1,2 , which is a key aspect in catalysis. An advantage of such studies is that the nano-colloidal systems are easy to monitor spectroscopically, as opposed to bulk solid-state samples where chiroptical spectroscopy is challenging 48 . One important message from this work is that although chiral crystals have been considered as sources for generation of homochirlity in biomolecules, the opposite effect of biomolecules inducing homochirality in crystals is also fascinating.…”

Mueller matrix microscope with a dual continuous rotating compensator setup and digital demodulation

“…The intensity detected by every pixel of the camera is frequency analyzed by digital demodulation. To our knowledge, this is the first time it has been done, as the typical strategy used by imaging instruments that measure complete MMs was based in the combination of the intensities measured at several fixed orientations of the compensators [23] or the liquid crystals [24,25]. This sequential, "step-by-step" method is well established and it is relatively easy to implement because the camera only needs to take an image at some predetermined positions of the compensators (usually 16 different positions).…”

Measurement of the optical activity of anisotropic samples by transmission Mueller matrix ellipsometry

“…where m 00 , m 11 , m 22 , m 33 are in most cases close to 1 1 . For these type of samples a measurement of the Mueller matrix elements m 03 and m 12 (or m 30 and −m 21 ) give, respectively, a direct measurement of CD and CB.…”

“…However, it is well-known that if the studied medium presents linear birefringence or linear dichroism, the standard approaches to measure optical activity may fail because none of the Mueller matrix elements is a direct measurement of CD or CB. In this condition the measurement of single elements of the Mueller matrix gives complicate mixtures of different optical effects rather than pure values of CD or CB [1]. a e-mail: oarteaga@ub.edu 1 This is true for media without large CD or CB, i. e. in almost all samples where the optical activity has a molecular origin.…”