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Updated: Jul 26, 2025
High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
Published on: October 31, 2019
Thermochromism of rapid responses to temperature changes versus mechanochromism in a Ni-dithiolene complex salt
Lei Xu1, Yi-Ming Wang1, Zi-Heng Feng1
1State Key Laboratory of Materials-Oriented Chemical Engineering and College of Chemistry and Molecular Engineering, Nanjing Tech University, Nanjing 211816, P. R. China. yinqian@njtech.edu.cn.
Abstract:
A thermochromic or mechanochromic material can switch between at least two stable states in response to changes in temperature or static pressure/strain. In this study, we investigated a Ni-dithiolene dianion salt, 1,1'-diheptyl-4,4'-bipyridinium bis(maleonitriledithiolato)nickelate (1), and found that its cations and anions stack alternately to form a uniform mixed stack. These mixed stacks then combine to form a molecular solid through Coulomb and van der Waals interactions. Upon heating, 1 undergoes a reversible phase transition at around 340/320 K during the first heating/cooling cycle, resulting in rapid thermochromism with a color change from green (stable state) to red (metastable state) within a few seconds. This is the first report of a crystal of bis(maleonitriledithiolato)nickelate(II) salt with green color. Additionally, 1 exhibits irreversible mechanochromism, intense near-IR absorbance, and a dielectric anomaly. The structural phase transition is responsible for these properties, as it induces alterations in the π-orbital overlap between the anion and cation within a mixed stack. The intense near-IR absorbance arises from the ion-pair charge transfer transition from [Ni(mnt)2]2- to 4,4'-bipyridinium.
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