Exploring the Localized-to-Delocalized Transition in Mixed Valence Ruthenium Polypyridines

PAOLA S. OVIEDO; GERMAN E. PIESLINGER; ALEJANDRO CADRANEL; BRUNO M. ARAMBURU TROSELJ; LUIS M. BARALDO

Buenos Aires

Conferencia; Humboldt Colloquium; 2018

Alexander von Humboldt-Stiftung

Electron transfer (ET) is ubiquitous in chemical, physical and biological systems, and plays a key role in catalysis and energy conversion. Mixed-valence systems very often present inter-valence charge transfer absorption bands (IVCT), whose energy and shape are related to the pathway that drives the electron from one center to the other. Thus, IVCT bands have been studied to evaluate the impact of different variables -redox potentials, nature of the bridge, donor-acceptor distance, solvent interactions, ionic strength- on the electron transfer process.It has been predicted that the decoupling of the solvent modes from the ET rate may be achieved by freezing the solvent in which the ET is occurring. The main effect of this decoupling is that solvent dipolar reorientation will no longer play a dynamic role in the reorganization of the system and the ET will only depend of a weighted average of intramolecular vibrations. Therefore, the rate of ET is expected to increase as the solvent temperature decreases. However, this increase in rate should only occur at the freezing point of each solvent and then change no further (i.e. solvent modes decouple once frozen and remain uncoupled).It may be argued that the sometimes bewildering I, II, II/III, III classification schemes may be abolished in due course despite their historical significance during the development of the field. Instead, the proper characteristics of the mixed valence complexes should be used to define the symmetry and the barrier for valence exchange for each experimental method considering the appropriate time frames.The original purpose for explore the properties of mixed-valence complexes in the localized-to-delocalized borderline was the possibility to study intramolecular electron transfer between equivalent metal sites in a stable, well-defined coordination compound. Later aspects involved the test-system character of such species for electron-transfer theory and for spectroscopic techniques. Given that electron transfer between organized functional atoms or molecules is an essential process within the rapidly growing field of molecular electronics there have been proposals to use mixed-valence systems for controlled charge propagation (?molecular wires?) and for information processing (?molecular switching?) within molecular devices.For this project, our goal is to synthesize and explore the electronic properties of cyanide-bridged ruthenium polypyridines. We study the electronic coupling between the metal centres, using UV-vis-NIR, IR and EPR spectroscopy, and DFT calculations. The spectroelectrochemistry technique allow us to explore the different redox states of these systems in several solvent at different temperatures in order to find the best candidates for future use as sensors or catalysts.