Research - Overview
In 1669, Erasmus Bartholin called the doubling of an image viewed through Iceland spar "one of the greatest wonders that nature has produced." More than three centuries later, the interactions of crystals with light continue to produce wonder in our laboratories. Why study crystals and light? Nature offers few pairs of substances of common experience so different -- crystals are concrete geometric entities and light is most ethereal -- that work so well at informing one another.
Every civilization has invented technologies for dyeing textile fibers. The dyeing of growing crystals is likewise a general branch of supramolecular chemistry but one that never developed into an independent area of inquiry. We have used colored and luminescent molecules as optical probes of crystal growth mechanisms in quite the same way the biologically minded chemists have used luminescent labels or probe molecules to study the specificity of non-covalent interactions in cells. Dye crystals can be excellent substrates for single molecule spectroscopies and can be used as single photon sources for quantum information technologies. In order to determine the structure of our colorful mixed crystals we have been required to invent new microscopies and in turn have discovered new crystal-optical phenomena.
The science of crystal optics is surely not complete. For example, researchers have struggled to measure chiroptical properties of organized substances. Recent advances in polarimetry by Kobayashi and Kaminsky now allow us to determine the orientational dependence of optical rotation and circular dichroism - measurements formerly restricted to fluids - in crystals and molecules. Together with advances in quantum chemistry, it is now possible to provide structural interpretations of chiroptics. Current research is focused on the optical rotatory power of H2O. The dearth of information on the anisotropy of chiroptical properties represents an enormous hole in the science of molecular chirality.
While we understand a good deal about how single crystals grow, we are on shaky ground with respect to understanding mechanisms of the assembly of regular polycrystalline substances. These phenomena are much more complex. For example, spherical crystalline aggregates are common in Alzheimer's disease, supercooled high polymers, and many simple molecular substances. These so-called spherulites commonly display supramolecular chirality. Here, new methods in polarimetric imaging are used to understand the mesoscale stereochemistry of complex, regular crystal aggregates.