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

A combined spectroscopic and theoretical study on a ruthenium complex featuring a π\pi-extended dppz ligand for light-driven accumulation of multiple reducing equivalents

International audienceThe design of photoactive systems capable of storing and relaying multiple electrons is highly demanded in the field of artificial photosynthesis, where transformations of interest rely on multielectronic redox processes. The photophysical properties of the ruthenium photosensitizer [(bpy)$_2$Ru(oxim-dppqp)]$^{2+}$ (Ru), storing two electrons coupled to two protons on the pi-extended oxim-dppqp ligand under light-driven conditions, are investigated by means of excitation wavelength-dependent resonance Raman and transient absorption spectroscopies, in combination with time-dependent density functional theory; the results are discussed in comparison to the parent [(bpy)$_2$Ru(dppz)]$^{2+}$ and [(bpy)$_2$Ru(oxo-dppqp)]$^{2+}$ complexes. In addition, this study provides in-depth insights on the impact of protonation or of accumulation of multiple reducing equivalents on the reactive excited states

Multifunctional Polyoxometalate-Platforms for Supramolecular Light-driven Hydrogen Evolution

Multifunctional supramolecular systems are a central research topic in light-driven solar energy conversion. Here, we report a polyoxometalate (POM)-based supramolecular dyad, where two platinum-complex hydrogen evolution catalysts are covalently anchored to an Anderson polyoxomolybdate anion. Supramolecular electrostatic coupling of the system to an iridium photosensitizer enables visible light-driven hydrogen evolution. Combined theory and experiment demon-strate the multifunctionality of the POM, which acts as photosensitizer / catalyst-binding-site and facilitates light-induced charge-transfer and catalytic turnover. Chemical modification of the Pt-catalyst site leads to increased hydrogen evolution reactivity. Mechanistic studies shed light on the role of the individual components and provide a molecular understanding of the interactions which govern stability and reactivity. The system could serve as a blueprint for multifunctional polyoxometalates in energy conversion and storage

Pyrimidoquinxoalinophenanthroline opens next chapter in design of bridging ligands for artificial photosynthesis

Using a dehydrogenative chemistry on the complex approach, a new polypyridine bridging ligand that bridges the gap of already existing systems is synthesized. By the usage of versatile cross-coupling reactions two different coordination spheres are included in the ligand architecture. Due to the twisted geometry of the novel ditopic ligand, the resultant division of the ligand in two distinct subunits leads to steady state as well as excited state properties of the corresponding mononuclear Ru(II) polypyridine complex resembling those of prototype [Ru(bpy)3]2+ (bpy = 2,2´-bipyridine). The localization of the initially optically excited and the nature of the long-lived excited states on the Ru-facing ligand spheres is evaluated by resonance Raman and fs-TA spectroscopy, respectively, and supported by DFT and TDDFT calculations. Coordination of a second metal (Zn or Rh) to the available bis-pyrimidyl-like coordination sphere strongly influences the frontier molecular orbitals apparent by e.g., luminescence quenching. Thus, the new bridging ligand motif offers electronic properties which can be adjusted by the nature of the second metal center. Using the heterodinuclear Ru-Rh complex, visible light-driven reduction of NAD+ to NADH was achieved, highlighting the potential of this system for photocatalytic applications