Synthesis and Electrochemiluminescence of a Ru(bpy)₃-Labeled Coupling Adduct Produced on a Self-Assembled Monolayer

In this work, a series of silicon chips containing sputtered gold electrodes were first coated with a self-assembled monolyayer (SAM) of lipoic acid. The same electrodes were then functionalized by using a Ru(bpy)₃²⁺ amine derivative, bis(2,2‘-bipyridine)-[4-(4‘-methyl-2,2‘-bipyridin-4-yl)aminobutyl] ruthenium bis(hexafluorophosphate). Its synthesis and purification is reported in detail for the first time. A two-step preparation of the emitting layer increased both the compactness of the SAM and the density of Ru emitting sites, as evidenced by electrochemiluminescence (ECL) and X-ray photoelectron spectroscopy (XPS) investigations. This approach enables the preparation of reproducible and compact ECL-active monolayers containing bulky molecules without the need for preliminary purification of the labeled surfactant. The occurrence of the coupling surface reaction was detected by monitoring the electrochemically induced luminescence from the modified electrode, in the presence of tripropylamine as oxidative co-reactant, and was confirmed by time-of-flight secondary ion mass spectrometry and XPS measurements.