Rate-Determining Step in the Electrogenerated Chemiluminescence from Tertiary Amines with Tris(2,2‘-bipyridyl)ruthenium(II)

Abstract

The rates and mechanism of coreactant electrogenerated chemiluminescence (ECL) from tris(2,2‘-bipyridyl)ruthenium(II) (Ru(bpy)3 2+) and the tertiary amines, tripropylamine (TPrA) and trimethylamine (TMeA), in aqueous solution were investigated. Transient (0.5 ms) potential steps were used with microelectrodes to investigate the emission time course under a variety of solution conditions. With amine concentrations that are low with respect to Ru(bpy)3 2+, the emission rises continually during the transient potential step and decays slowly after its termination. In contrast, the emission approaches a plateau during the potential step and is rapidly extinguished afterward with concentrations of Ru(bpy)3 2+ that are much lower than the amine concentration. At intermediate pH values, the emission intensity increases approximately linearly with pH. The emission after the potential step is unaffected by the rest potential. To simulate these temporal characteristics by finite difference methods, a mechanism employing 15 discrete chemical and electrochemical steps was employed, using literature-based thermodynamic values and electron-transfer rate constants evaluated from Marcus theory. The rate-limiting step was found to be the deprotonation of the amine radical cation. In addition, the simulations required a rate constant for the homogeneous oxidation of the tertiary amine by electrogenerated Ru(bpy)3 3+ value much below its Marcusian-calculated value to match the experimental data.

Control of Excitation and Quenching in Multi‐colour Electrogenerated Chemiluminescence Systems through Choice of Co‐reactant

“…The rates of the respective electron‐transfer quenching will be dependent on not only the exergonicity of the reactions, but also the relative concentrations and lifetimes of the respective reactants 7. 10a Quenching of the [Ir(ppy) 3 ]* excited state is thus exacerbated by the longer lifetime (1.9 μs, compared to 1.1 μs for [Ru(bpy) 3 ] 2+ *) 6h. Moreover, the different extent of the ‘switch‐off’ of [Ir(ppy) 3 ] ECL at high overpotentials by TPA, DIPEA‐OH and DIPEA may also be influenced by the relative lifetimes of the respective aminium radicals 10a.…”

Theory and Simulation for Optimising Electrogenerated Chemiluminescence from Tris(2,2′‐bipyridine)‐ruthenium(II)‐Doped Silica Nanoparticles and Tripropylamine

“…Based on Marcus theory, this suggests that their reorganisation energies and unspecific work terms are similar. On the other hand, even if their thermodynamic driving forces cannot be compared with precision since the standard redox potential of TPrA * oxidation remains still unknown with precision (< À1.7 V vs Ag/AgCl), [37] they are both highly exergonic with Gibbs enthalpies being both on the order of ca. À0.2 eV.…”

Characterization of electrochemiluminescence of tris(2,2′-bipyridine)ruthenium(II) with glyphosate as coreactant in aqueous solution

“…The step for the generation of an excited state *Ru(bpy) 3 2+ in eq 7 is known to be relatively fast (a value of k' ≈ 10 10 M -1 s -1 in Ru(bpy) 3 2+ /TPA system) [19]. If the substrate of GLPY is electroinactive and eq 6a is supposed to be the rate determining step (rds), kinetic and mechanistic information can be derived from the variation of the As can be seen in Fig.…”