An Exceptional Thermally Induced Four-State Nonlinear Optical Switch Arising from Stepwise Molecular Dynamic Changes in a New Hybrid Salt


Switching materials in channels of nonlinear optics (NLOs) are of particular interest in NLO material science. Numerous crystalline NLO switches based on structural phase transition have emerged, but most of them reveal a single-step switch between two different second-harmonic-generation (SHG) states, and only very rare cases involve three or more SHG states. Herein, we report a new organic-inorganic hybrid salt, (Me3NNH2)(2)[CdI4], which is an unprecedented case of a reversible three-step NLO switch between SHG-silent, -medium, -low, and -high states, with high contrasts of 25.5/4.3/9.2 in a temperature range of 213-303 K. By using the combined techniques of variable-temperature X-ray single-crystal structural analyses, dielectric constants, solid-state C-13 nuclear magnetic resonance spectroscopy, and Hirshfeld surface analyses, we disclose that this four-state switchable SHG behavior is highly associated with the stepwise-changed molecular dynamics of the polar organic cations. This finding demonstrates well the complexity of molecular dynamics in simple hybrid salts and their potential in designing new advanced multistep switching materials.



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Zeng, Y; Hu, CL; Xu, WJ; Zeng, TW; Zhu, ZX; Chen, XX; Liu, DX; Chen, YJ; Zhang, YB; Zhang, WX; Chen, XM

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This work was supported by the NSFC (22071273, 21805312, and 21821003) and Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program (2017BT01C161). Y.Z. is thankful to the Graduate Innovation Fund of Sun Yat-Sen University (19lgyjs34). We appreciate the assistance from the Instrumental Analysis & Research Center, Sun Yat-Sen University with the EA analysis.

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