Z) under biased condition. Fig. 5(c) shows Raman spectra at different position of OFG device under different bias condition. Microscopic image in Fig.5(b) of OFG device shows colour change only on the negative electrode of the device. During the electrochemically reduction, intensity of color between E$_1$-E$_2$ and on E$_1$ electrode changed which attributes reduction of EV$^{2+}$ molecule.

The corresponding Raman scattering studies have been done on E$_1$ and E$_2$. Alphabets X, Y, Z on the microscopic images indicate the positions from where the Raman signals were collected. Raman spectrum in figure 5(c) X was recorded from the E$_1$ terminal of of an unbiased device, which shows major peak at 932 cm$^{2+}$, the peaks corresponding to EV$^{2+}$. Raman spectra 5(c)Y and 5(c)Z have been recorded under bias of -3.5V on E$_1$ and E$_2$ respectively. Some additional peaks appear on the E$_1$ electrode in biased condition, spectrum 5(c)Y shows two prominent peaks corresponding to reduced viologen which are at 1028 and 1528 cm$^{-1}$. With biasing potential, peak intensity is increases as the applied potential increases which shows the formation of more free radical cations (EV$^{\newmoon +  }$ )There is no change in the spectrum recorded on E$_2$ where +ve terminal of the 