Nonlinear optical ionic liquids

Molecular orbital calculations indicate that molecules with a high electron density diffused over a large volume will have third order nonlinear optical activity. Anions often have higher second hyperpolarizability values(gamma) than similar neutral molecules. Also, molecules or ions containing higher row elements have higher gammas. Salts with cations that have their positive charge only weakly interacting with the anion also enhance the third order nonlinear optical activity. That looks like the recipe for ionic liquids. A number of sulfur-containing mono- and dianion salts were synthesized and characterized through Z-scan measurements. Most were ionic liquids, and some showed significant third order nonlinear optical behavior. The general features of ionic liquids such as wide liquidus range, good thermal stability, and low vapor pressure are particularly advantageous for applications of nonlinear optical materials. Potential applications are in optical limiting and other all-optical devices.