The electrochemical reduction of triphenylethylene in DMSO: a mechanistic study using mercury hemispherical microelectrodes

Abstract

The electrochemical reduction of triphenylethylene (TriPE) was studied in dimethylsulfoxide (DMSO) containing 0.1M tetra-n-butylammonium perchlorate supporting electrolyte through the use of cyclic voltammetry. Experiments were conducted using two different mercury hemisphere electrode sizes (radii 3 and 25μm) and with TriPE concentrations of 0.50 and 2.00mM so as to span fully the transition from convergent to linear diffusion and steady state to transient voltammetry. Voltammetric responses obtained display two sucessive reduction waves with formal potentials separated by ca. 290mV. Taking the diffusion coeffient of TriPE, TriPE− and TriPE2− to be 2.8×10−10m2s−1, excellent fits between simulation and experiments were obtained across all experimental conditions, with the following DISP2 reaction scheme:Heterogeneous reactions:TriPE+e-⇌TriPE-k10=0.15cms-1,α1=0.5TriPE-+e-⇌TriPE2-k20=0.032cms-1,α2=0.5(Ef,20-Ef,10=290mV)Homogeneous reactions:TriPE−+TriPE−⇌TriPE+TriPE2−KDISP=1.3×10−5,kf,DISP=5.0×104mol−1dm3s−1TriPE2-→productsKeq>1.5×106,kf>1.0×106s-1where k0 denotes the standard electrochemical rate constant, α the transfer coefficient, Ef0 the standard formal potential, KDISP the equilibrium constant of the disproportionation reaction, kf,DISP the rate of the forward reaction of disproportionation, Keq the equilibrium constant of the decay of TriPE2−, and kf the rate of the forward reaction of the decay of TriPE2−.