Analytical Sciences

Abstract − Analytical Sciences, 32(4), 443 (2016).

Electrochemiluminescence of Tris(2,2′-bipyridyl)ruthenium(II) with Ascorbic Acid and Dehydroascorbic Acid in Aqueous and Non-aqueous Solutions
Fumiki TAKAHASHI,* Kaoru HATTORI,** Masanori MATSUOKA,** and Jiye JIN**
*Center for Energy and Environmental Science, Interdisciplinary Cluster for Cutting Edge Research, Shinshu University, 3-1-1 Matsumoto, Nagano 390-8621, Japan
**Department of Chemistry, Faculty of Science, Shinshu University, 3-1-1 Matsumoto, Nagano 390-8621, Japan
The electrochemiluminescence (ECL) of tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+) is studied in non-aqueous media using dehydroascorbic acid (DHA) as coreactant to validate the evidence for the mechanism of the ascorbic acid (H2A)/Ru(bpy)32+ ECL system in an aqueous media. DHA is electrochemically reduced around –1.2 V vs. Ag/Ag+ in pure acetonitrile to generate the ascorbyl radical anion (A•−), which is confirmed by in-situ UV-visible absorption measurements using a thin-layer spectroelectrochemical cell. The ECL of the DHA/Ru(bpy)32+ system in non-aqueous media is not observed in the potential range from 0 to +1.4 V in anodic potential sweep mode; however, distinct ECL is detected using double potential step electrolysis from –1.2 to +1.4 V vs. Ag/Ag+. The ECL may be generated by a homogeneous charge-transfer process between A•− produced during the first pulse potential step (–1.2 V) and Ru(bpy)33+ generated during the second pulse potential step (+1.4 V). The calculated standard enthalpy (–ΔH°) for the charge-transfer reaction between A•− and Ru(bpy)33+ is 2.29 eV, which is larger than the lowest excited singlet state energy of Ru(bpy)32+ (*Ru(bpy)32+; 2.03 eV, 610 nm). It is determined that the generated intermediate A•− is crucial in the Ru(bpy)32+ ECL reaction.