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High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
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pH-Dependent Switching Between Nonlinear-Optical-Active Nitrate-Based Supramolecular Polymorphs
Qiao Xia1, Xingxing Jiang2, Chunbo Jiang1
1China-Australia Joint Research Center for Functional Molecular Materials, School of Chemical Science and Engineering, Tongji University, Shanghai, 200092, China.
Angewandte Chemie (International Ed. in English)
|March 1, 2025
Summary
Researchers developed a novel pH-modulation strategy to synthesize three non-centrosymmetric (NCS) nitrate supramolecular polymorphs. This method controls secondary bonds, enabling tailored nonlinear optical (NLO) properties in these advanced materials.
Area of Science:
- Materials Science
- Crystallography
- Nonlinear Optics
Background:
- Synthesizing non-centrosymmetric (NCS) second-order nonlinear optical (NLO) crystals, especially metastable polymorphs, is difficult due to complex interactions.
- Controlling crystal structures is key to achieving desired NLO properties.
Purpose of the Study:
- To report the first synthesis of three nitrate supramolecular polymorphs (α-, β-, and γ-phases) using a pH-modulation secondary-bond strategy.
- To investigate the influence of pH on secondary bond orientation and its effect on crystal packing and NLO properties.
Main Methods:
- Utilized a pH-modulation strategy to assemble π-conjugated planar primitives ([C2H5N4] and [NO3]).
- Varied solution pH to control secondary bond orientation and influence crystal lattice packing.
- Investigated polymorph transformations (e.g., 2D α-phase to 2D β-phase) and their impact on NLO responses.
Main Results:
- Successfully synthesized three nitrate supramolecular polymorphs (α-, β-, and γ-phases) with varying NCS characteristics.
- Demonstrated that pH-induced secondary bond variations dictate crystal packing and can lead to different NLO properties.
- Observed distinct second harmonic generation (SHG) responses and birefringences in the α- and β-phases, linked to hydrogen-bond layer stacking.
Conclusions:
- Secondary-bond interactions are crucial for forming rare nitrate supramolecular polymorphs and controlling their structures.
- The pH-modulation strategy provides a new paradigm for developing high-performance NCS materials with tailored optical properties.
- Elucidated supramolecular polymorph transition mechanisms and structure-property correlations for NLO materials.
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