Synthesis and characterization of a series of carbazole-based monolithic photorefractive molecules

A series of monolithic photorefractive molecules forming organic glasses with low glass transition temperature (−2–69 °C) was synthesized starting from 9-(2-ethyl-hexyl)-carbazole. These molecules show distinct photoconductivity due to the carbazole moiety and obvious optical nonlinearity owing to the push–pull structure. Some of these molecules can form transparent films with good stability and excellent optical quality. The absorption of the molecules is more or less red-shifted depending on the strength of the donor–acceptor internal charge transfer. A molecule with a highly asymmetric structure using both a nitrobenzene and a cyano group as the electron-withdrawing components (M2) shows the best photorefractive performance, its gain coefficient was measured as high as 266 cm−1 at an applied electric field of 42 V/μm without any extra sensitizer while the FWM efficiency was measured to be 5% at electric fields of 27 V/μm.