Use of Ru(bpy)32+/tertiary aliphatic amine system fast potential pulses electrochemiluminescence at ultramicroelectrodes coupled to electrochemical data for evaluating E° of amine redox couples

The electrochemiluminescent (ECL) reaction mechanism of the tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+) with six tertiary aliphatic amines, namely, tri-n-butylamine (TBuA), tri-iso-butylamine (TisoBuA), tri-n-propylamine (TPrA), methyl-di-n-propylamine (MeDPrA), tri-ethylamine (TEtA) and tri-methylamine (TMeA) in aqueous solution was examined using fast potential pulses at carbon fiber microelectrodes and with simulation techniques with the aim to obtain information on the E° value of the amine redox couples. Pulse time was chosen so as emission occurred after the potential pulse end. The experimental approach to estimate the E° values of the amine redox couples consisted in combining electrochemical and ECL data under the assumptions that at least one amine E° value is available and that the proposed reaction mechanism well represents the experiment. TPrA was used as reference compound (E° = 0.88 V versus SCE) and from this, 1.05 ± 0.04 V (TMeA), 0.92 ± 0.04 V (TEtA), 0.91 ± 0.03 V (MeDPrA), 0.79 ± 0.03 V (TBuA) and 0.72 ± 0.03 V (TisoBuA) were the estimated E° values of the other amines. The TEtA E° value (also known from the literature) is equal within the indicated experimental errors and gives information on the accuracy of the proposed method. Moreover, was possible to confirm the already proposed order of magnitude of the rate determining step of the ECL process through the evaluation of two experimental parameters, A% (number of photons percent recorded at the inversion time, tinv) and Tr (relative position of the peak emission with respect to tinv). The ksh value of the considered amines was estimated close to 10−3.5 cm s−1 comparing emissions at Pt ultramicroelectrode.