Kim Mark, Kim Yong Min, Moon Hong Chul
Department of Chemical Engineering, University of Seoul Seoul 02504 Republic of Korea
RSC Adv. 2020 Jan 2;10(1):394-401. doi: 10.1039/c9ra09007j. eCollection 2019 Dec 20.
Viologens are one of the most well-known electrochromic (EC) chromophores. In particular, symmetric dialkyl viologens have been widely used in EC devices (ECDs), but suffer from the formation of viologen radical cation dimers that deteriorate device performance. In this work, we propose an effective route to suppress dimer formation through molecularly altering one of the N-substituents. We prepare 1-benzyl-1'-heptyl viologens and find that such asymmetric molecular structures attribute to the suppression of dimer production when used as EC chromophores. The suppression of dimer formation allows us to drive the device at relatively higher voltages, so that we could achieve viologen-based ECDs showing large transmittance changes between colored and bleached states, efficient and fast coloration, and stable coloration/bleaching cyclic operation. The results indicate that high-performance ECDs can be realized by utilizing viologens containing asymmetric molecular structures.
紫精是最著名的电致变色（EC）发色团之一。特别是，对称二烷基紫精已被广泛应用于电致变色器件（ECD）中，但会形成紫精自由基阳离子二聚体，从而降低器件性能。在这项工作中，我们提出了一种通过分子改变其中一个N-取代基来抑制二聚体形成的有效途径。我们制备了1-苄基-1'-庚基紫精，并发现当用作EC发色团时，这种不对称分子结构有助于抑制二聚体的产生。二聚体形成的抑制使我们能够在相对较高的电压下驱动器件，从而实现基于紫精的ECD，其在着色和漂白状态之间显示出较大的透光率变化、高效快速的着色以及稳定的着色/漂白循环操作。结果表明，利用含有不对称分子结构的紫精可以实现高性能的ECD。
