Different lights, different selectivies: Luminescence of a new guanidinium 3,3′‐functionalized bipyridyl–Ru^II complex has been studied for sensing of several anions. L‐Glutamate and dihydrogenphosphate are both detected by photoluminescence and electrochemiluminescence. However, the complex displays differential selectivities for these anions depending on the sensing channels (see scheme).

A new guanidinium 3,3′‐functionalized bipyridylruthenium(II) complex has been prepared for the differential sensing of L‐glutamate and dihydrogenphosphate anions depending on the luminescent detection scheme. The effects of such anions on the photoluminescent (PL) and electrochemiluminescent (ECL) properties of the complex have been investigated and compared. The PL intensity increases up to fourfold 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, ECL emission of the Ru^II complex is initiated at 1.45 V versus Ag/AgCl/KCl and the ECL intensity increases only in the presence of dihydrogenphosphate. Indeed, L‐glutamate is already oxidized at the relatively high potential required for ECL generation and thus it does not affect the ECL signal. The comparison of the competitive ECL and PL assays in a mixture of anions confirms the differential detection of L‐glutamate and of dihydrogenphosphate. Thus, both sensing channels (i.e., PL and ECL) show different selectivities depending on the nature and on the electroactivity of the target anions. Multianion analysis is demonstrated in competitive assays using complementary detection methods.