Nonlinear Optical Anisotropy of Highly Oriented Poly(p-Phenylene Benzobisthiazole)Langmuir-Blodgett Films

Poly(p-phenylene benzobisthiazole) (PBT) has received a strong attention as a nonlinear optical (NLO) material because of its large, ultrafast NLO response1 and inherently superior physical and chemical properties2. However, the material is difficult to process into thin film with good optical quality, which hindered the detailed and accurate NLO studies. In order to improve optical quality, the PBT Langmuir-Blodgett (LB) films were fabricated via a novel precursor route. The PBT LB films show not only improved optical quality but also highly in-plane oriented molecular packing. Because the π-electrons are delocalized along the polymer chain direction, the highly oriented packing of the polymer chains results in linear and NLO anisotropy properties. Therefore, in-plane anisotropy measurement of optical third-harmonic generation (THG) is one of the powerful tools to elucidate the packing arrangement in LB films of one-dimensional conjugated system.