However, TDMQ20 has two pKa values pKa1=1.0 and pKa2=8.0 . Therefore, the two peaks are not related to the protonation change of TDMQ20. The splitting of peaks was observed for azo dye compounds derived from hydroxyquinolinone, and the authors of that study suggest the accompaniment of some adsorption component. Interestingly, on DPV and CV at lower scan rates (v = 10 mV/s, pH 6.0 and 5.0, see SI Figure .6.), only one signal is observed. This suggests that the electron transfer process is quite fast and a higher scan rate was needed to observe the double peak. In order to investigate the cathodic electrochemical behaviour of TDMQ20, the potential range of the CVs was extended to negative potentials. Cyclic voltammograms were recorded from +0.2 V to -0.8, and up to +0.9 V (Figure ) or, in the reverse direction, from +0.2 V to +0.9 V and then a sweep to a negative potential of -0.8 V (Figure ). When the measurement started at +0.2 V and moved toward negative potentials, a reduction peak with very low current intensity was observed (Figure ). An increase in the pH value of the supporting electrolyte caused a shift of the reduction peak towards more negative potential values (Figure . Figure CV for TDMQ20 at pH 7.4 in two directions (A) 0.2 to -0.8 V up to 0.9 V and (B) from 0.2 to 0.9 up to -0.8V recorded in 0.1 M phosphate buffer, v = 0.1 V/s.