Exploring the Full Potential of Photocatalytic Carbon Dioxide Reduction Using a Dinuclear Re2Cl2 Complex Assisted by Various Photosensitizers

Photosensitizing units have already been applied to enable light-driven catalytic reduction of CO2 with mononuclear rhenium complexes. However, dinuclear catalytic systems that are able to activate CO2 in a cooperative bimetallic fashion have only rarely been combined with photosensitizers. We here present detailed studies on the influence of additional photosensitizers on the catalytic performance of a dirhenium complex (Re2Cl2) and present correlations with spectroscopic measurements, which shed light on the reaction mechanism. The use of [Ir(dFppy)3] (Ir, dFppy=2-(4,6-difluorophenyl)pyridine)) resulted in considerably faster CO2 to CO transformation than [Cu(xant)(bcp)]PF6 (Cu, xant=xantphos, bcp=bathocuproine). Emission quenching studies, transient absorption as well as IR spectroscopy provide information about the electron transfer paths of the intermolecular systems. It turned out that formation of double reduced species [Re2Cl2]2− along with an intermediate with a Re−Re bond ([ReRe]) can be taken as an indication of multi-electron storage capacity. Furthermore, under catalytic conditions a CO2-bridged intermediate was identified.German Research FoundationDFG http://dx.doi.org/10.13039/501100001659Peer Reviewe

Trendbericht: Photochemie

Die photochemische Forschung entwickelt unter anderem Photo(redox)katalysatoren, farbstoffsensibilisierte Solarzellen (DSSCs) und lichtemittierende Dioden (LED). Solche Systeme benötigen Moleküle, die Sonnenlicht absorbieren und für chemische Reaktionen nutzbar machen oder in definierten Wellenlängenbereichen emittieren. Bisher waren dies meist Edelmetallkomplexe. Ein Ziel ist es, Komplexe zu entwickeln, die billigere und besser verfügbare Metalle enthalten. Vielversprechende Ergebnisse gibt es für Systeme mit Kupfer, Mangan, Nickel, Molybdän, Zink und Chrom

Imidazo-Phenanthroline Ligands as a Convenient Modular Platform for the Preparation of Heteroleptic Cu(I) Photosensitizers

The capture and storage of solar energy is a promising option to overcome current energy issues. To put such systems into practice, molecular photosensitizers should be based on abundant metals and possess a strong absorption capability for visible light. Therefore, a systematic series of four novel heteroleptic Cu(I) complexes of the type [(P^P)Cu(N^N)]+ (with P^P = xantphos and N^N = different diimine ligands) has been prepared. As an essential feature, these copper photosensitizers contain an imidazole moiety at the backbone of the diimine ligand, which increases the aromatic π-system compared to phenanthroline type ligands. Moreover, 2-(4-bromophenyl)-1-phenyl-1H-imidazo-[4,5-f][1,10]phenanthroline was used as a starting point and modular platform for gradually extended diimine ligands. Suzuki cross-coupling was applied to introduce different kind of substituents in the back of this ligand. Afterwards, a combination of NMR spectroscopy, mass spectrometry, X-ray analysis, cyclic voltammetry, UV/vis and emission spectroscopy was used to investigate the structural, electrochemical and photophysical properties of these compounds. As a result, a reversible reduction, strongly increased extinction coefficients and significantly redshifted absorption maxima (>20 nm) were found compared to traditional Cu(I) photosensitizers without an imidazo moiety. Moreover, these compounds show a bright emission in the solid state