geometry (CBG). Similar device was fabricated by drop casting EV in between two gold electrodes separated by few microns where both the electrodes are on the same plane. Schematic to show both the geometries are shown in Fig. S1 in the supplementary information (SI). OFG device is used for in-situ Raman spectroscopy with electrical circuit arrangement to see the molecular change by applying bias. Raman spectroscopy experiments in OFG device and result clearly revealed connection between electrochemical doping and Raman peak position. Both UV-Vis and Raman spectroscopic data reconcile the correlation between charge carriers and color changes in viologen base devices. The free radical cation has been depicted as the fundamental charged species responsible for the color changing properties in ethyl viologen. Appropriate control experiments have been carried out to validate the conclusions.

![Figure 2: In-situ UV-Vis spectroscopy to show changes in transmittance of the CFG device by applying bias in the range of 0 to -3.5V. Inset showing colour appearance of the device at various potential.](figure2){width="10cm"}

Experimental Details
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Commercially available chemicals from Alfa Aesar and Sigma Aldrich were used for preparing samples in the present study. Polyethylene oxide (PEO, Alfa Aesar, MW = 100 000), Ethyl viologen diperchlorate 