(Spectro)electrochemically monitoring adsorption of EDOT oligomers at the aqueous|TFT interface. The cationic nature of the adsorbed EDOT oligomers is proven by the negative shift of the PZC for the differential capacitance curve obtained after two CV cycles (Fig. , dashed line) compared to that before cycling (Fig. , solid line). Saturation of the interfacial region with a sufficiently high density of EDOT oligomers of the critical chain length required to induce their adsorption at the L|L interface occurs by the 3 rd cycle, as evidenced by the appearance of the sharp negative peak at ca. -0.1 V associated with the exchange between TB -and SO4 2-(labelled β in Fig. ). This anion exchange process is also seen in the differential capacitance curve obtained after two CV cycles when the scan direction Further proof of the adsorption of EDOT oligomers at an applied Δ o w 𝜙 of -0.1 V was provided by spectroelectrochemical measurements (Fig. ). In situ UV/vis absorption spectra in total internal reflection mode (TIR-UV/vis) were recorded at the polarisable L|L interface using the cell described in Fig. . The spectra were first recorded as the applied Δ o w 𝜙 was held at +0.4 V for 20 s. At this potential, an increase of absorbance at ∼400 nm was seen with time (Fig. ). This signal corresponds to the formation of short EDOT oligomers in the organic EDL due to IET between Ce 4+ and EDOT monomers. Based on the position of the absorption band, it is likely that the majority of the EDOT oligomers comprise of four monomer units or less. When the applied Δ o w 𝜙 was stepped to -0.1 V for 20 s, a significant red shift in the absorbance spectrum was observed due to an increase in oligomer conjugation length (Fig. ). The absorbance spectrum at -0.1 V is characteristic of a p-doped PEDOT thin film, as shown in Supplementary Fig. All spectra were recorded at ambient, aerobic conditions.