Polymer Displays Extreme Birefringence

By taking advantage of the modular nature of coordination polymers, Daniel B. Leznoff, Zuo-Guang Ye, and coworkers at Simon Fraser University, Burnaby, British Columbia, have designed a polymeric material that is among the most birefringent solids ever observed (Angew. Chem. Int. Ed. 2007, 46, 8804). Birefringence, or double refraction, is the difference in the refractive index of light along two perpendicular directions in a material. The phenomenon is commonly observed in some crystals. For example, when a calcite crystal is placed onto a printed page, the letters appear doubled. The researchers decided to try their hand at making birefringent polymeric materials, which they say could be tailored for a range of optical applications. The team's polymers are made up of lead or manganese terpyridine complexes that are strung together by cross-linking silver or gold cyanide units to form a two-dimensional lattice. The polymers' birefringence reaches values up to 0.43, compared with 0.17 for calcite.