Monolithic NLO chromophores with different pendant groups and matrix-assisted-poling effect: Synthesis and characterization

Realization of the large electro-optic (EO) activity for organic nonlinear optical (NLO) chromopores with high first order hyperpolarizability requires simultaneous optimization for molecular structure. In this work, we investigated the influences of different pendant groups in chromophore's side chains on the performance of EO materials. A series of NLO chromophores F1-F3 based on the same conjugated structure but with different pendant groups have been synthesized and systematically investigated. Due to the disperse-red type pendant groups, chromophore F3 shows excellent film-forming ability and relatively high glass transition temperature without blending with optically inactive polymer matrix. The Variable Angle Spectroscopic Ellipsometry (VASE) measurement proves the neat F3 film displays a higher index of refraction value and weak absorption at 1310 nm and 1550 nm, which is beneficial for reducing the operation voltage and optical loss of modulator. Due to the effective isolating ability of pendant groups, the best EO coefficient of the poled F3 film reaches to 81 pm/V, which is two times larger than the value of the same type chromophore in guest-host material. This result, together with high index of refraction and low optical loss, will shed light on a new perspective for the design of new monolithic organic EO materials.