导电聚合物由于其优异的性能而受到广泛关注，包括优异的化学稳定性，热和氧化稳定性、可调节的电性能、催化能力、光学和机械特性等。导电聚合物用于多种应用：传感器、抗静电涂层、发光二极管、晶体管、柔性设备，以及电致变色设备中的活性材料，例如调节透光量的“智能”窗口。

聚（3，4-亚乙基二氧噻吩），也称为PEDOT，是市场上最具价值的导电聚合物之一。这是由于其高导电性、电化学稳定性、催化性能、在几乎所有常见溶剂中的高不溶性以及有趣的电致变色性能（在掺杂状态下透明，在中性状态下着色）。在应用报告主要说明如何使用光谱电化学技术对PEDOT薄膜进行评估。

Raman spectroelectrochemistry was employed for the fingerprint characterization of the different oxidation states, neutral and doped, of PEDOT deposited on the Au SPE. The spectrum of the neutral state was obtained at -0.40 V (Figure 2, blue line) and p-doped PEDOT at +0.50 V (Figure 2, red line) in a 0.1 mol/L lithium perchlorate (LiClO₄) aqueous solution.

Assignments of the vibrational modes for each Raman band are listed in Table 2. The characteristic vibrational modes depend on the polymer oxidation state, particularly those located in the Raman shift region (1100–1600 cm^-1). Several Raman bands of PEDOT are up-shifted in the doped state. Note that although the C_α-C_α’ inter-ring stretching vibrational mode is not detected in neutral PEDOT, it is observed at 1293 cm^-1 in the doped state.

Valuable qualitative information provided by UV-Vis spectroelectrochemistry allows the complete characterization of the PEDOT film previously deposited on the gold working electrode. Spectroelectrochemical experiments were performed in a 0.1 mol/L LiClO₄ aqueous solution, scanning the potential from 0.00 V to +0.70 V and back to -0.40 V at 0.05 V/s for two cycles. UV-Vis spectra were recorded in reflection configuration (300 ms integration time), resulting in almost 300 spectra collected during the electrochemical experiment. Synchronization of the electrochemical and spectroscopic responses is completely assured by the SPELEC instrument.

Cyclic voltammetry (Figure 3a) does not show any remarkable electrochemical peaks associated with the change of the oxidation state of PEDOT. However, a UV-Vis band centered at 525 nm is clearly observed in the simultaneously recorded spectra (Figure 3b).

Evolution of the absorption band at 525 nm with changing potential is shown in Figure 4. Initially, absorbance decreases from 0.00 V to +0.70 V. In the backward scan, absorbance increases up to -0.40 V and decreases until 0.00 V, where it reaches a similar value as was at the beginning of the experiment. In the second scan, the spectroscopic signal shows the same spectroelectrochemical behavior. Absorbance at 525 nm at -0.40 V achieves the same value in both cycles, demonstrating the stability of this film for at least two cycles.

Evolution of this absorbance band with potential agrees with the electrochromic properties of PEDOT, being colorless in the doped state at positive potentials, while it is colored in the neutral state at negative potentials.

Figure 5 displays the relevant derivative voltabsorptogram (dAbs/dt vs. potential) at 525 nm. The derivative curve is only related to the faradaic component of the concomitant current flow. As can be observed in Figure 5, this derivative curve proves the polymer doping and de-doping processes through its reversible behavior.