Analytical Electrogenerated Chemiluminescence

excitation reactions (vide infra).3][14] From a historical point-of-view, the roots of this research are found in the electrochemical generation of aromatic hydrocarbon radical ions, because the dominant dogma promoted in organic chemistry at that time was that the electrons go by pairs and not one by one, as largely demonstrated since then. 4Hercules reported first the 'production of chemiluminescence during electrolysis of aromatic hydrocarbons'. 12He obtained 'electrochemically generated luminescence' from several hydrocarbons such as anthracene, pyrene, rubrene in N,N-dimethylformamide (DMF) or acetonitrile solvents by using two main configurations: (1) by alternating the current or (2) by applying a current at two closely spaced electrodes. 12This short seminal report contains remarkable original ideas and suggestions on the stability of the electrogenerated species, the possible mechanisms, the experimental configurations, ECL imaging as illustrated by the ECL photograph of the concentric electrode grids, etc.This work was published almost simultaneously with another article on CL electron-transfer reactions obtained by recombination, i.e. annihilation, between anion and cation radicals of 9,10-diphenylanthracene (DPA) that were prepared chemically. 11A few months later, the same group published annihilation ECL of electrogenerated DPA radicals. 13This example shows how ECL and CL histories are intrinsically related, as also illustrated by other examples in the following decades. 11,15-22Indeed, CL and ECL processes are similar in nature.They share some common features and theoretical fundamentals (see Chapter 2). 23,24It is interesting to note that E. A. Chandross mentioned that 'a chemiluminescent reaction between electro-generated anthracene positive and negative radical ions has been observed by Hoijtink and co-workers' (private communication during a visit in the summer of 1963). 11However, these results were never published by G. J. Hoijtink.The groups of Chandross and Bard used cyclic voltammetry to study the anodic and cathodic processes of these aromatic hydrocarbons and thus to clarify the annihilation mechanism leading to ECL emission. 13,14These initial works have been rapidly followed by many other practical and theoretical developments.Some of the keymilestones in this context are depicted in Scheme 1.1, which is certainly a very subjective and non-exhaustive list of examples.For instance, [Ru(bpy) 3 ] 21 is a model ECL luminophore that is largely used even nowadays and Tokel and Bard reported in the 1970s the first example of ECL derived from electrogenerated species of the [Ru(bpy) 3 ] 21 complex. 164][25] The discovery of ECL emission in aqueous media 26 with efficient coreactants (see Chapter 4) such as tri-n-propylamine (TPrA) 22 has led to successfully commercialized bioassays for clinical diagnostics (see Chapter 15). 27,28The early ECL studies were based on ion annihilation and this fundamental research was essential to pave the way for coreactant ECL, which is almost exclusively used nowadays for (bio)analytical applications.