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 (H
2A)/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 (–Δ
H°) 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.
View full abstract