a result of applied bias is due to the EV$^{\newmoon +  }$ species being generated at the –ve terminal as a result of reduction of EV$^{2+}$. By combining the data in Figs 2, 5 & 3S, one can see that the Raman spectrum from the dark region on the device (E$_1$ electrode in Fig. 5(a)) shows the presence of EV$^{\newmoon +  }$ species whereas the virgin device shows the signature of stable EV$^{2+}$. Therefore, the Raman spectra permit the conclusion that the mechanism of bias induced color change in the electrochromic device is due to formation of free radical cation from viologen dication.

Above discussion confirms the origin of color change in the electrochromic device. It will be interesting to see how fast and how many times the electrochromic device be turned ON and OFF. Figure 6 shows ON and OFF cycles in terms of normalized absorbance corresponding to 580 nm which has been studies within a specific time period\[34\]. Initially at 580 nm, on zero bias absorbance is in its lowest value, Al which reaches the highest value Ah by applying potential (-3.5V) making it opaque for this wavelength. Figure 6 shows that device can be turned ON and 