Stable second-order NLO semi-IPN system based on bipyridine-containing polyimide and alkoxysilane dye

Abstract

An organosoluble polyimide based on bipyridyl moiety and an alkoxysilane dye have been developed for second-order non-linear optics (NLOs). This bipyridine-containing polyimide exhibits a glass transition temperature of 254 degrees C and a degradation temperature of 400 degrees C. An NLO-active semi-interpenetrating network (IPN) system was prepared by blending the polyimide with the alkoxysilane dye via in situ sol-gel process of alkoxysilane. The selection of this bipyridine-containing polyimide as the polymeric matrices provides improved solubility and thermal stability, and most importantly enhanced intermolecular interactions. No aggregation of the NLO chromophores in the polyimide matrices was observed through morphology and NLO studies. Under the limitation of chromophore degradation at elevated temperatures, the pristine poled/cured alkoxysilane dye exhibits poorer long-term stability. By introducing the polyimide upon a silica network by the semi-IPN system, randomization of the oriented chromophores can be effectively suppressed. Using in situ contact poling, the r(33) coefficients of 2.2-17.0 pm/V were obtained for the optically clear semi-IPN NLO materials. Excellent temporal stability (100 degrees C) was also achieved for these semi-IPN materials. Copyright (c) 2005 John Wiley & Sons, Ltd.