Sui Qi, Wang He-Chong, Zhang Yan-Yan, Sun Rong, Jin Xin-Xin, Wang Bing-Wu, Wang Lin, Gao Song
Key Laboratory of Surface &, Interface Science of Polymer Materials of Zhejiang Province, School of Chemistry and Chemical Engineering, Zhejiang Sci-Tech University, Hangzhou, 310018, P. R. China.
Center for High Pressure Science (CHiPS), State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao, Hebei, 066004, P. R. China.
Chemistry. 2023 Aug 25;29(48):e202301575. doi: 10.1002/chem.202301575. Epub 2023 Jul 20.
Manipulating the radical concentration to modulate the properties in solid multifunctional materials is an attractive topic in various frontier fields. Viologens have the unique redox capability to generate radical states through reversible electron transfer (ET) under external stimuli. Herein, taking the viologens as the model, two kinds of crystalline compounds with different molecule-conjugated systems were designed and synthesized. By subjecting the specific model viologens to pressure, the cross-conjugated 2-X all exhibit much higher radical concentrations, along with more sensitive piezochromic behaviors, compared to the linear-conjugated 1-X. Unexpectedly, we find that the electrical resistance (R) of 1-NO decreased by three orders of magnitude with the increasing pressure, while that in high-radical-concentration 2-NO remained almost unchanged. To date, such unusual invariant conductivity has not been documented in molecular-based materials under high pressure, breaking the conventional wisdom that the generations of radicals are beneficial to improve conductivity. We highlight that adjusting the molecular conjugation modes can be used as an effective way to regulate the radical concentrations and thus modulate properties rationally.
在固体多功能材料中，通过控制自由基浓度来调节其性能是各个前沿领域中一个引人关注的课题。紫精具有独特的氧化还原能力，能够在外部刺激下通过可逆电子转移（ET）产生自由基态。在此，以紫精为模型，设计并合成了两种具有不同分子共轭体系的晶体化合物。通过对特定的模型紫精施加压力，与线性共轭的1-X相比，交叉共轭的2-X均表现出更高的自由基浓度以及更敏感的压致变色行为。出乎意料的是，我们发现随着压力增加，1-NO的电阻（R）下降了三个数量级，而在高自由基浓度的2-NO中其电阻几乎保持不变。迄今为止，在高压下基于分子的材料中尚未有这种异常的电导率不变性的报道，这打破了自由基的产生有利于提高电导率的传统观念。我们强调，调整分子共轭模式可以作为一种有效方法来调节自由基浓度，从而合理地调控材料性能。
