PHOTOREFRACTIVE POLYMER COMPOSITE TRAPPING PROPERTIES AND A LINK WITHCHROMOPHORE STRUCTURE

The photorefractive properties and the phase stability of polymer comp osites are dependent on the detail of the alkyl chain substituent atta ched to the electro-optic dye within the composite. Photorefractive co mposites based on poly (N-vinylcarbazole) (PVK), sensitized with trini trofluorenone (TNF) and mixed with a concentration of 47.5 wt. % of el ectro-optic dye have been tested for photorefractive performance. Two alternative azo dyes of identical molecular weight have been used to p roduce alternative composites; both dyes were modified to suppress spa tial isomerism and incorporated an eight carbon alkyl chain at the ele ctropositive end of the chromophore: either a straight octyl chain or a branched ethylhexyl chain was substituted. The reorientational enhan cement of photorefractive performance is similar in the composites res ulting from these dyes. The dye with a straight octyl chain led to a c omposite with improved holographic performance. The dye with a branche d ethylhexyl chain led to a composite exhibiting lower diffraction eff iciency, but with superior phase stability. A tentative explanation is offered for these differences based on the shape of the alkyl substit uent and its effect on a trapping mechanism involving the dye molecule s and the sensitisor anions in PVK: TNF-based photorefractive composit es. (C) 1998 American Institute of Physics. [S0021-8979(98)10023-3]