  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.
