applications spanning from photochemistry and solar energy conversion, molecular wire and switches. Recently viologen has been used as single molecular transistor Viologen is used as chemical quencher for improvement of quantum yield of nanoemitter\[23\]. Viologens are frequently used as electrochemical label, photochemical probe or in studies on the electron-transport processes or oxidative damage in DNA\[24\].

In the present work a simple electrochromic device has been fabricated in two geometries to study the fundamental reason of colour change. A clear understanding may enable one to get other colors than blue. In depth studies have been done by observing bias induced changes in EV species using spectroscopic techniques in-situ. The in-situ experiments helps in understanding the underlying mechanism for bias induced color change which is required for making a versatile electrochromic device. Nondestructive spectroscopic techniques like Raman and UV-Vis may prove to be handy in analyzing the mechanism for the same. The two geometries used to understand the bias induced color change enables us to carry out in-situ measurements for an in-depth analysis. In the simplest geometry, the EV (in an appropriate matrix) has been sandwiched between two Indium Tin Oxide (ITO) electrodes on quartz substrate to get the device in cross-bar 