*Suryakant Mishra, Haardik Pandey, Priyanka Yogi, Shailendra K. Saxena, Swaroop Roy, Pankaj R. Sagdeo and Rajesh Kumar*[^1]

Material Research Laboratory, Discipline of Physics & MSEG, Indian Institute of Technology Indore, Simrol-453552, Madhya Pradesh, India

ABSTRACT

Fabrication and operation of simple solid state electrochromic devices using ethyl viologen diperchlorate in a polymer matrix is presented here. In-situ Raman and transmission/absorption studies have been done to establish the origin of bias induced color change, between a transparent and navy blue color, in the electrochromic device. The origin of bias induced color change has been attributed to the bias induced redox switching between its viologen dication and free redicle forms. Fundamental reason behind colour changes of viologen molecule has been established. In-situ UV-Vis spectra reveals that the navy blue color of the device under biased condition is not due to increase in the transparency corresponding to blue wavelength but due to suppression of the transparency corresponding to the complementary colors. Absorption modulation has been reported from the device with good ON/OFF contrast of the device.

**Keywords:** Raman spectroscopy, UV-Vis spectroscopy, Viologen, Electrochromism

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Introduction
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An electrochromic device, as name suggests, is a device which changes color as a result of an electrical 