Thermal-Stable and High-Performance Organic Nonlinear Optical Chromophores for Advanced Electro-Optic Modulators

To address the challenge of developing organic second-order nonlinear optical materials that combine high electro-optic (EO) coefficients with excellent thermal stability, four novel chromophores (designated BHG1 to BHG4) are designed and synthesized. These chromophores feature two types of steric hindrance groups-tert-butyldimethylsilyl (TBDMS)-bisphenol fluorene and pentafluorobenzyl (PB)-bisphenol fluorene-into the aniline donor architecture. The incorporation of these bulky substituents not only substantially elevates the glass transition temperatures (T_g >130 °C) of all four chromophores but also markedly enhances their long-term alignment stability. Among them, BHG2 and BHG4, functionalized with a strongly electron-withdrawing trifluoromethyl-tricyanofuran (CF₃-TCF) acceptor, demonstrate exceptional propensity for self-assembling into a high-quality thin film. The neat chromophore BHG2 achieves a remarkable EO coefficient of 304 pm V^-1, which is attributed to the suppressed dipole-dipole interactions. A high-speed electro-optic modulator has been fabricated using the neat BHG2 exhibiting a low half-wave voltage-length product (V_πL) of 2.80 V mm and a 3 dB bandwidth exceeding 40 GHz. These results underscore the significant potential of these materials for advanced optoelectronic devices.