Forum for Science, Industry and Business

Tailored for Optical Applications

When a calcite crystal is placed onto a printed page, the letters appear doubled. This is the result of a property called birefringence. Scientists at the Simon Fraser University in Canada have now developed a material that is among the most birefringent solids ever observed. As described in the journal Angewandte Chemie, this material is not a mineral, but rather a coordination polymer.

Refraction is the change in direction of a wave of light when it passes from air into water or a crystal. It is caused by a local change in the speed of propagation. In the case of birefringence, the light is divided into two perpendicularly polarized beams, which move at different speeds and exit the material shifted relative to each other. The source of this effect is a crystal lattice that has different optical properties along its various axes (anisotropy).

Birefringent optical components are usually made of calcite. The critical value for these applications is the difference in the refractive index of light in two directions in the crystal, the birefringence, which is 0.17 for calcite.

The team led by Daniel B. Leznoff and Zuo-Guang Ye has now produced a highly birefringent coordination polymer. Coordination polymers are one-, two-, or three-dimensional bridged metal complexes. The advantage to this type of compound is the limitless number of design possibilities: The individual components—metal center, chelating ligands, and bridging ligands—can be selected and combined almost at will to get the desired material properties.

Leznoff’s team, spearheaded in the lab by Michael J. Katz, decided to use a “terpy” ligand, a flat ring system consisting of three pyridine units (six-membered aromatic rings with one nitrogen atom), and lead as the metal center. The complexes are linked by linear bridging ligands made of a central silver or gold ion and two cyanide groups to form two-dimensional layers. If the central lead atom is replaced with manganese, one-dimensional ladder-like structures are formed. Within their crystals, however, the lead and manganese polymers have analogous arrangements: the terpy molecules are piled up plane-to-plane, perpendicular to the axis of crystal growth. This is clearly the crucial factor leading to the high birefringence, which reaches values from 0.43 to just under 0.4, significantly higher than those of the numerous inorganic birefringent materials.

Improved optical data storage and data transfer in communications technology are possible applications for such highly birefringent materials.

Author: Daniel B. Leznoff, Simon Fraser University (Canada), http://www.sfu.ca/leznoffgroup/

Title: Highly Birefringent Materials Designed Using Coordination-Polymer Synthetic Methodology

Angewandte Chemie International Edition 2007, 46, No. 46, 8804–8807, doi: 10.1002/anie.200702885

Daniel B. Leznoff | Angewandte Chemie
Further information:
http://www.sfu.ca/leznoffgroup/
http://pressroom.angewandte.org

Im Focus: Regensburg physicists watch electron transfer in a single molecule

For the first time, an international team of scientists based in Regensburg, Germany, has recorded the orbitals of single molecules in different charge states in a novel type of microscopy. The research findings are published under the title “Mapping orbital changes upon electron transfer with tunneling microscopy on insulators” in the prestigious journal “Nature”.

The building blocks of matter surrounding us are atoms and molecules. The properties of that matter, however, are often not set by these building blocks...

Im Focus: University of Konstanz gains new insights into the recent development of the human immune system

Scientists at the University of Konstanz identify fierce competition between the human immune system and bacterial pathogens

Cell biologists from the University of Konstanz shed light on a recent evolutionary process in the human immune system and publish their findings in the...

Im Focus: Transformation through Light

Laser physicists have taken snapshots of carbon molecules C₆₀ showing how they transform in intense infrared light

When carbon molecules C₆₀ are exposed to an intense infrared light, they change their ball-like structure to a more elongated version. This has now been...

Im Focus: Famous “sandpile model” shown to move like a traveling sand dune

Researchers at IST Austria find new property of important physical model. Results published in PNAS

The so-called Abelian sandpile model has been studied by scientists for more than 30 years to better understand a physical phenomenon called self-organized...

Im Focus: Cryo-force spectroscopy reveals the mechanical properties of DNA components

Physicists from the University of Basel have developed a new method to examine the elasticity and binding properties of DNA molecules on a surface at extremely low temperatures. With a combination of cryo-force spectroscopy and computer simulations, they were able to show that DNA molecules behave like a chain of small coil springs. The researchers reported their findings in Nature Communications.

DNA is not only a popular research topic because it contains the blueprint for life – it can also be used to produce tiny components for technical applications.