Self-Assembled Monolayers of Redox-Active 4d-4f Heterobimetallic Complexes

In this work, we report the preparation of functional interfaces incorporating heterobimetallic systems consisting in the association of an electroactive carbon-rich ruthenium organometallic unit and a luminescent lanthanide ion (Ln = Eu and Yb). The organometallic systems are functionalized with a terminal hexylthiol group for subsequent gold surface modification. The formation of self-assembled monolayers (SAMs) with these complex molecular architectures are thoroughly demonstrated by employing a combination of different techniques, including infrared reflection absorption spectroscopy, ellipsometry, contact angle, and cyclic voltammetry measurements. The immobilized heterobimetallic systems show fast electron-transfer kinetics and, hence, are capable of fast electrochemical response. In addition, the characteristic electrochemical signals of the SAMs were found to be sensitive to the presence of lanthanide centers at the bipyridyl terminal units. A positive shift of the potential of the redox signal is readily observed for lanthanide complexes compared to the bare organometallic ligand. This effect is equally observed for preformed complexes and on-surface complexation. Thus, an efficient ligating recruitment of europium and ytterbium cations at gold-modified electrodes is demonstrated, allowing for an easy electrochemical detection of the lanthanide ions along with an alternative preparative method of SAMs incorporating lanthanide cations compared to the immobilization of the preformed complex.