Photoinduced electron transfer in dyads and triads with d6 metal complexes and anthraquinone

Abstract

Over the past years, designing molecular systems that mimic natural processes has become the center of much research in the field of chemistry. Many of these artificial systems are synthesized in order to study photoinduced intramolecular electron transfer. These models are usually consisting of a photosensitizer, an electron acceptor, and/or an electron donor, and are considered attractive candidates for the conversion and storage of solar energy. The molecular dyads investigated in this thesis are comprised of a d6 metal diimine complex acting as photosensitizer and an anthraquinone as electron acceptor. In addition to the d6 metal photosensitizer and the anthraquinone acceptor, a tertiary amine has been used as an electron donor in the triads. Photoexcitation of these systems in presence of a strong hydrogen-bond donor strongly influences the thermodynamics and kinetics of the photoinduced electron transfer reaction. In fact, hydrogen-bonding between protic solvent and reduced anthraquinone has a great impact on the excited state deactivation of the dyads by electron transfer from ruthenium to anthraquinone. In the triads, this hydrogen-bonding leads to a significant increase of the lifetime of the charge-separated state containing an oxidized tertiary amine and reduced anthraquinone. This long-lived charge-separated state is interesting in terms of storing light energy in chemical bonds. In both the dyads and triads, the overall photoinduced reaction in presence of protic solvent may be regarded as a variant of stepwise proton-coupled electron transfer (PCET) in which proton density is transferred from the hydrogen-bond donor solvent to photoreduced anthraquinone.