Electrochemiluminescence for differential anions sensing

Electrochemiluminescence (ECL) is initiated by an electron transfer at the electrode surface and it ends with the light emission from an electronically excited states.[1, 2] In other words, the initiation of the phenomenon is an electrochemical step, whereas the analytical information is usually contained in the light signal. Thus ECL combines intimately electrochemical and photochemical aspects. The increasing interest in ECL over the past two decades is refl ected in the growing number of its analytical applications.[ 1,2] The most extensively investigated ECL luminophores are tris(2,2’-bipyridyl)ruthenium(II) and its derivatives. The attractive feature of these systems is that they contain built-in chromophores and redox sensing sites, with chemical stability, redox properties, excited-state reactivity, and luminescent emission. Recently, Ru(II)bipyridyl complexes containing crown ether moieties have been used as ECL analytical tool for metal cations sensing.[3–5] However, currently, there are no method describing the ECL detection of anions that are not implicated in redox reaction generating the excited state. We present a new guanidinium 3,3’-functionalized bipyridyl ruthenium(II) complex (Figure 1A) that has been prepared for the diff erential sensing of L-glutamate and dihydrogenphosphate anions depending on the luminescent detection scheme.[6] Luminescence of a new guanidinium 3,3’-functionalized bipyridyl Ru(II) complex has been studied for diff erential sensing of several anions. The eff ects of anions on the photoluminescent (PL) and ECL properties of the complex have been investigated and compared. The PL intensity increases up to 4-fold in the presence of L-glutamate. The increase of intensity in the presence of dihydrogenphosphate is weaker and no change in PL intensity is observed in presence of acetate, iodide or chloride anions. With n-tripropylamine (TPrA), ECL emission of the Ru(II) complex is initiated at 1.45 V vs. Ag/AgCl/KCl. ECL activity with TPrA shows a completely diff erent behavior for these anions which are not directly involved in the ECL process. Indeed, only dihydrogenphosphate is detected by ECL. ECL intensity increases by adding it to the solution (Figure 2A). The addition of L-glutamate does not modify the ECL intensity (Figure 2B). Indeed, L-glutamate is already irreversibly oxidized at the very anodic potential required for the ECL initiation and therefore this compound is not able to bind to the modifi ed complex. Acetate, iodide and chloride anions do not modify the PL intensity neither ECL. So, from an analytical point of view, it means that [Ru(bipy)2L]4+ displays differential selectivities for these anions depending on the sensing channels. It is thus possible to detect and to discriminate between diff erent anions by cross-correlating the luminescence detection channels.