Synthesis and characterization of photorefractive polymer containing electron transport material

An acrylate type monomer was prepared by the reaction of 2-hydroxyethyl acrylate with 9-oxo-9H-thioxanthene-3-carboxylic acid 10,10-dioxide and was polymerized using AIBN as an initiator and N,N-dimethylformamide as a solvent to yield a polymer containing a thioxanthene unit (P-THEA). The resulting polymer had a number-average molecular weight of 18 000 and a glass-transition temperature of 113 degrees C. Photorefractive (PR) composites consisting of P-THEA as an electron-transporting component, 4-N,N-diethylamino-E-beta-nitrostyrene (DEANST) as a nonlinear optical chromophore, and butyl 9-oxo-9H-thioxanthene-3-carboxylate 10,10-dioxide (TH-Bu-n) as a plasticizer were prepared. These composites had an absorption coefficient of 11-33 cm(-1) at 633 nm and glass-transition temperature of 32-42 degrees C. A PR device with a thickness of 100 mu m was fabricated by sandwiching the PR composite between two ITO coated glasses. The electric field and DEANST concentration dependencies of the gain coefficients and diffraction efficiency were investigated by two-beam coupling and four-wave mixing methods. The electron-transporting nature of PR composite was confirmed by the comparison of the sign of coupling coefficient with that of a PVK-based composite.