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 (CF 3 ‐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 π L) 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.