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 = Eu³⁺ and Yb³⁺). 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.

Fluorenylporphyrins functionalized by electrochromic ruthenium units as redox-triggered fluorescence switches

The electrofluorochromic behaviour of two ruthenium-appended porphyrin dyads has been investigated. Differences in response according to the nature of the interposed aryl linker are rationalised with the aid of electrochemistry and TD-DFT calculations.

Redox-Active Chiroptical Switching in Mono- and Bis-Iron Ethynylcarbo[6]helicenes Studied by Electronic and Vibrational Circular Dichroism and Resonance Raman Optical Activity

Introducing one or two alkynyl-iron moieties onto a carbo[6]helicene results in organometallic helicenes (2 a,b) that display strong chiroptical activity combined with efficient redox-triggered switching. The neutral and oxidized forms have been studied in detail by electronic and vibrational circular dichroism, as well as by Raman optical activity (ROA) spectroscopy. The experimental results were analyzed and spectra were assigned with the help of first-principles calculations. In particular, a recently developed method for ROA calculations under resonance conditions has been used to study the intricate resonance effects on the ROA spectrum of mono-iron ethynylhelicene 2 a.

Redox-driven porphyrin based systems for new luminescent molecular switches

This work explores the possibility of controlling the fluorescence of porphyrins via oxidation of a ruthenium acetylide unit. The modulation depends on the nature of the porphyrin unit(s).

Exploring the self-assembly and energy transfer of dynamic supramolecular iridium-porphyrin systems

We present the first examples of dynamic supramolecular iridium–zinc porphyrin systems.

Photoinduced electron transfer as a design concept for luminescent redox indicators

The exploitation of photoinduced electron transfer as a general design principle for the development of luminescent redox indicators and logic gates is described. Potential future applications in biology, environmental analysis, biomedical diagnostics, corrosion science and materials science are mentioned.

New donor–acceptor conjugates based on a trifluorenylporphyrin linked to a redox–switchable ruthenium unit

Spectroelectrochemical studies show four accessible redox states on dyad 3 with the first oxidation process taking place at the Ru(ii) centre and the second oxidation and first reduction processes at the porphyrin centre.