Molecular design and synthesis of branched bichromophore-attached linear fluorinated polyimides for nonlinear optical applications

A branched structure bichromophore was developed to increase the nonlinearity of optical polymers. The branched bichromophore was incorporated into the polymer backbone to prepare a novel nonlinear optical (NLO) side-chain fluorinated polyimide with high optical nonlinearity and good thermal stability. The novel nonlinear optical side-chain fluorinated polyimide exhibits a large electro-optic (E-O) coefficient (γ33) (34 pm/V at 1550 nm) which is larger than that of the conventional side-chain optical polyimide. This is mainly attributable to an increased chromophore concentration and high polarizing efficiency derived from the branched structure. The branched structure of the bichromophore is incorporated into a polymer backbone to result in a high chromophore concentration. Moreover, the three-dimensional (3D) architecture and large molecular size of the branched bichromophore can spatially shield from strong interchromophore electrostatic interactions to enhance the poling efficiency. The side-chain fluorinated polyimide exhibits excellent solubility in common organic solvents, good film-forming property, high glass-transition temperature (Tg) (190 °C) and thermal stability up to 235 °C.