An electrochemical study of the oxidation of 1,3,5-Tris[4-[(3-methylphenyl)phenylamino]phenyl]benzene

Abstract

An investigation into the oxidative electrochemistry of 1,3,5-Tris[4-[(3-methylphenyl)phenylamino]phenyl]benzene (TMPB) is described. In particular, the heterogeneous electron-transfer kinetics in N, N-dimethylformamide (DMF) and dichloromethane (DCM) are studied using the high-speed microband channel electrode. Experiments to investigate the standard electrochemical rate constants, k 0, transfer coefficients, α, and formal potentials, E f 0, of the observable oxidations of TMPB in both DMF and DCM solutions containing 0.10 M tetrabutylammonium perchlorate (TBAP) are reported for 12.5 μm platinum microband electrodes using a range of linear flow velocities from 12 to 25 m s −1. The measured values of k 0 for the two measurable oxidations in DMF are 1.03 ± 0.41 and 1.02 ± 0.20 cm s −1, and for the three oxidations in DCM are 0.44 ± 0.04, 0.17 ± 0.03 and 0.08 ± 0.02 cm s −1, respectively. The values of α for these oxidations in DMF are 0.48 ± 0.06 and 0.52 ± 0.02, and in DCM are 0.52 ± 0.02, 0.62 ± 0.03 and 0.53 ± 0.07, respectively. The respective formal oxidation potentials (all measured vs Ag) are 0.533 ± 0.002 and 0.766 ± 0.003 V in DMF, and 0.161 ± 0.002, 0.495 ± 0.002 and 1.128 ± 0.004 V in DCM. The presence of the monocation radical in DCM is confirmed by ESR measurement. Experiments are also presented to explore the voltammetry of TMPB in microdroplets of toluene and also in the solid-phase, when in contact with aqueous solutions of sodium fluoride, perchlorate, nitrate and sulphate. It was found that, when TMPB is dissolved in a toluene microdroplet, anion insertion accompanies the first oxidation for the case of perchlorate and nitrate, with anion-facilitated dissolution occurring for sulphate and fluoride. More complex reactions occur at more positive potentials. In the solid-phase, however, slow anion-facilitated dissolution still occurs for fluoride and sulphate, and rapid direct dissolution takes place in the case of perchlorate.