Survey of Enhanced, Thermally Stable, and Soluble Second-Order Nonlinear Optical Azo Chromophores

A series of mono- and bisazo dyes were synthesized to obtain soluble, thermally stable, and enhanced second-order nonlinear optical chromophores (NLOphores). To prepare good sol-gel films, the most important factor was the solubility of NLOphores. Those azo NLOphores showing sufficient solubility were further classified into three groups: non-nitro-containing, nitro-containing, and fluorine-containing derivatives. Though non-nitro-containing NLOphores showed high solubility, their second-order nonlinearity was low. Nitro-containing NLOphores showed a rather high Td and a medium nonlinearity. Fluorine-containing NLOphores, especially perfluoroalkylsulfonyl derivatives, showed high nonlinearity and a rather low Td.