Scientific Achievement
In January 2024, a new approach for constructing organic piezoelectric materials was proposed by the team of Shan Jiang from Shanghai Tech University and Wei Li from Nankai University. They utilized porous organic cages (POCs) as a platform for building organic piezoelectric materials, constructing piezoelectric crystals through post-synthesis modifications and anion regulation. Support during the data collection process was provided by the BL10U2 Crystallography Beamline at the Shanghai Synchrotron Radiation Facility (SSRF).
Significance and Impact
In recent years, there has been increasing research interest in flexible, environmentally friendly, and biocompatible organic piezoelectric materials. The efficient conversion of mechanical energy to electrical energy using organic piezoelectric materials has garnered widespread attention. However, the inherent tendency of organic crystals to crystallize in centrosymmetric space groups poses a significant barrier to realizing their piezoelectric potential. To overcome this obstacle, a new approach for constructing organic piezoelectric materials was proposed by the team of Shanshan Jiang from Shanghai Tech University and Wei Li from Nankai University. They utilized porous organic cages (POCs) as a platform for building organic piezoelectric materials, constructing piezoelectric crystals through post-synthesis modifications and anion regulation.
Research background
To obtain non-centrosymmetric organic cage crystals, the authors chose imine cages for post-synthesis modifications, resulting in amine cages with structural flexibility and low molecular symmetry. Subsequently, through protonation with anions of varying sizes and geometric configurations (Cl-, Br-, SO42-), the amine cages were transformed into organic cage salts. During the process of post-synthesis modifications, the conformation of the organic cage cations and the distribution of the anions were identified as the key factors determining crystal symmetry. Ultimately, five out of the six organic cage salts crystallized in non-centrosymmetric space groups, confirming the effectiveness of the imine cage post-synthesis modification strategy in yielding non-centrosymmetric crystals.
Main research contents
To investigate the structural properties of novel piezoelectric materials known as organic cage salts, the authors studied the crystal structural variations, nonlinear optical effects, and piezoelectric properties of these materials. By combining single-crystal X-ray diffraction with temperature-dependent second harmonic generation (SHG) tests, the researchers successfully observed a structural transition from non-centrosymmetric to centrosymmetric in RCC1-SO4 induced by anion displacement, which correlated with a "switching" behavior in the SHG signal. Furthermore, utilizing piezo response force microscopy (PFM), they observed a polarity reversal under voltage stimulation in RCC1-Cl, indicating the piezoelectricity and potential ferroelectric effects of organic cage salt materials. Following the determination of the piezoelectric properties of organic cage salts, the authors incorporated them into polymer composite films and further assembled them into flexible piezoelectric energy harvesters.
Bright Future Prospects
This novel class of organic piezoelectric materials exhibits excellent piezoelectric performance and holds significant potential applications in wearable devices, electronic skins, and biomedical sensing.
Figure 4: Due to their outstanding piezoelectric properties, POCs are ideal candidate materials for energy harvesting.
The related research findings were published under the title "Design of piezoelectric organic cage salts for energy harvesting" in Chem.
Contact
User contact for BL10U2 beamline: Qin Xu
E-mail: xuq@sari.ac.cn, TEL: 02120304908
Publication
Yang-zhi Ye，Hui-yu Liu，Yong-ji Gong，Ze-zhao Xu，Ying Zhao，Na Yu，Qi-sheng Wang，Wen Wen，Tie-ying Yang，Wei Li，Shan Jiang, Design of piezoelectric organic cage salts for energy harvesting, Chem, 10, 1–14(2024). [https://doi.org/10.1016/j.chempr.2023.12.006]
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