Energetic electrochemiluminescence of (9-fluorenyl)methanol induced by injection of hot electrons into aqueous electrolyte solution

Abstract

Hot electron injection into aqueous electrolyte solutions from metal/insulator/metal/electrolyte and metal/insulator/electrolyte tunnel junctions is considered and the possibility of an electrochemical generation of hydrated electrons is discussed. The hot electron-induced UV electrochemiluminescence of (9-Ñuorenyl)methanol was used to demonstrate the presence of highly energetic transient species in aqueous solution at several metal/insulator/electrolyte hot electron tunnel emitters. These transient species cannot be produced electrochemically in fully aqueous solutions at any active metal electrodes. A detailed mechanism for the present electrochemiluminescence is suggested.

Cathodic electrochemiluminescence of lucigenin at disposable oxide-coated aluminum electrodes

“…The effect of oxide film thickness on the ECL intensity is presented in Fig.3. The results are analogous to those previously observed with metal chelates and organic luminophores [25,33,43].…”

“…Based on our previous studies [22][23][24][25][26], hydrated electrons are assumed to be the primary reducing species to trigger most of the ECL reaction pathways studied by us so far. In alkaline conditions, ECL intensity started to slightly decrease when pH exceeded 9 due to the thinning of oxide film.…”

“…In previous studies [22][23][24][25][26], we have demonstrated that many kinds of luminophores can be excited by cathodic pulse-polarization at conductor/insulator/electrolyte (C/I/E) tunnel junction electrodes e.g. oxide-coated aluminum, silicon and magnesium electrodes.…”

“…General ECL excitation routes for luminophores based on our cathodic pulse polarization method have been observed to be reduction-initiated oxidative excitation (red-ox) or oxidation-initiated reductive excitation (ox-red) pathways in which the luminophores are excited by the cathodically generated species at the oxide film/electrolyte interface by successive one-electron transfer steps normally resulting in the luminophore in its original oxidation state but now in its singlet or triplet excited state [22][23][24][25][26]. However, sometimes the ECL mechanism is based on the decomposition of the luminophore [22].…”

“…In practice, cathodic reductions may be produced simultaneously by heterogeneously transferred electrons from the bottom of the conduction band of the insulating film, via the surface states of the insulating film and by presolvated hot and hydrated electrons [25]. Meanwhile, strongly oxidizing species such as sulfate and hydroxyl radicals can be cathodically generated from purposely-added coreactants or form dissolved oxygen [22,23,25,33,34]. In addition, F + -centers existing in oxide film of C/I/E electrodes may act as oxidants [2,23,33].…”