Zheng Huzhi, Zu Yanbing
Department of Chemistry, The University of Hong Kong, Pokfulam, Hong Kong, China.
J Phys Chem B. 2005 Jun 23;109(24):12049-53. doi: 10.1021/jp050350d.
We describe the influence of dissolved oxygen on the emission of Ru(bpy)3(2+) (bpy = 2,2'-bipyridine) by electrogenerated chemiluminescence (ECL) with tertiary amine as coreactant in aqueous solutions. The significance of the reactions between molecular oxygen and the ECL intermediate reducing radicals has been demonstrated for the first time. By varying the experimental conditions, the oxygen effect on different ECL routes of the Ru(bpy)3(2+)/tri-n-propylamine (TPrA) system was examined. When coreactant direct oxidation played a predominant role in producing ECL, the maximum emission intensity, especially that of the low-oxidation-potential (LOP) ECL, could change from O2-insensitive to highly O2-sensitive with decreasing TPrA concentration. This behavior can be interpreted as follows: A large excess of intermediate reducing radicals was produced at high [TPrA], and the dissolved oxygen within the ECL reaction layer was completely reduced by these radicals and exerted no quenching effect on the emission. At low [TPrA], however, coreactant oxidation generated a relatively small amount of reducing intermediates, and molecular oxygen acted as an interceptor, destroying the intermediates before they participated in the ECL pathways, which led to the obvious reduction of the emission intensity. In the latter case, the less efficient LOP ECL route was more remarkably affected. When ECL was generated primarily via the catalytic route at high [Ru(bpy)3(2+)], the reactions consuming the intermediate radicals by O2 became insignificant, and he drop of emission intensity in the presence of oxygen could mainly be ascribed to the excited-state quenching. A similar oxygen effect was also observed for the Ru(bpy)3(2+)/triethylamine (TEA) system.
我们描述了在水溶液中以叔胺作为共反应剂，通过电化学发光（ECL）研究溶解氧对Ru(bpy)3(2+)（bpy = 2,2'-联吡啶）发射的影响。首次证明了分子氧与ECL中间还原自由基之间反应的重要性。通过改变实验条件，研究了氧对Ru(bpy)3(2+)/三正丙胺（TPrA）体系不同ECL途径的影响。当共反应剂直接氧化在产生ECL中起主要作用时，随着TPrA浓度降低，最大发射强度，尤其是低氧化电位（LOP）ECL的发射强度，可从对O2不敏感变为对O2高度敏感。这种行为可以如下解释：在高[TPrA]时产生大量过量的中间还原自由基，ECL反应层内的溶解氧被这些自由基完全还原，对发射没有淬灭作用。然而，在低[TPrA]时，共反应剂氧化产生相对少量的还原中间体，分子氧充当拦截剂，在中间体参与ECL途径之前将其破坏，导致发射强度明显降低。在后一种情况下，效率较低的LOP ECL途径受到的影响更显著。当在高[Ru(bpy)3(2+)]时主要通过催化途径产生ECL时，O2消耗中间自由基的反应变得不显著，并且在有氧存在下发射强度的下降主要可归因于激发态淬灭。对于Ru(bpy)3(2+)/三乙胺（TEA）体系也观察到类似的氧效应。
