ICA trimer

We have previously considered [8,9] the redox behaviour and film structure of indole-5-carboxylic acid trimer (ICA trimer) films formed by the electrooxidation of indole-5-carboxylic acid (ICA, Fig. 11.2). We have shown that electrooxidation involves the production and deposition of an asymmetric cyclic trimer (Fig. 11.3) onto the electrode surface... 

ICA trimer films were produced by the electropolymerisation of 100 mM ICA in background electrolyte at + 1.46 V at the RDE, rotating at 4 Hz. Under these conditions [8,9], electrooxidation and film production occurs under steady-state current conditions at close to 100% current efficiency, and the film is expected to consist almost entirely of free trimer. The electrooxidation reaction was terminated after passing a charge of 173 mC. From equation (11.1) and (11.23) we calculate that this corresponds to 25 mC of redox charge or approximately 250 nmoles of deposited trimer. 

Figure 11.4 presents typical linear sweep voltammetry (LSV) data for the ICA trimer film. It is clear from these data that profound changes occur in the redox behaviour of the ICA trimer film on cycling. The freshly prepared film shows a square voltammogram, indicating that the coat has a large pseudocapacitance, with little evidence of redox peaks (Fig. 

It is clear from these data that an ICA trimer film undergoes profound changes in structure and redox kinetics on redox cycling and holding the coat in first the reduced then the oxidised form for long periods of time. Initially, we would expect, and our results are consistent with, a structure where the trimer is deposited in ir-conjugated stacks of oxidised trimer,... 

Ring-disc studies have confirmed [11] that for ICA between 7 and 9 electrons are passed and between 6 and 8 protons are evolved in the production of these films. This shows that the trimer is deposited in its oxidised form, with the incorporation of an anion from the electrolyte in order to preserve electroneutrality. 

---