Copper(I) Phosphinooxazoline Complexes: Impact of the Ligand Substitution and Steric Demand on the Electrochemical and Photophysical Properties.

A series of seven homoleptic CuI complexes based on hetero-bidentate P^N ligands was synthesized and comprehensively characterized. In order to study structure-property relationships, the type, size, number and configuration of substituents at the phosphinooxazoline (phox) ligands were systematically varied. To this end, a combination of X-ray diffraction, NMR spectroscopy, steady-state absorption and emission spectroscopy, time-resolved emission spectroscopy, quenching experiments and cyclic voltammetry was used to assess the photophysical and electrochemical properties. Furthermore, time-dependent density functional theory calculations were applied to also analyze the excited state structures and characteristics. Surprisingly, a strong dependency on the chirality of the respective P^N ligand was found, whereas the specific kind and size of the different substituents has only a minor impact on the properties in solution. Most importantly, all complexes except C3 are photostable in solution and show fully reversible redox processes. Sacrificial reductants were applied to demonstrate a successful electron transfer upon light irradiation. These properties render this class of photosensitizers as potential candidates for solar energy conversion issues.

Two Emissive Long-Lived Excited States of an Imidazole-Functionalized Ruthenium Dipyridophenazine Complex.

A ruthenium(II) polypyridine-type complex based on the dipyridophenazine ligand with a directly fused imidazole unit (L1, dipyrido[3,2-a:2',3'-c]phenazine-10,11-imidazole) has been synthesized, and its electrochemical and photophysical properties have been studied. The cyclic voltammogram of [Ru(tbbpy)2(L1)]2+ (C1) (tbbpy is 4,4'-tert-butyl-2,2'-bipyridine) shows a cathodic shift of the phenazine-based reduction process compared to similar molecules, while the first detected reduction wave (-1.34 V vs Fc/Fc+) is assigned to the imidazole unit within the molecule. On the basis of the TD-DFT calculations, the strong visible absorption band exhibited by C1 is assigned to a metal-to-ligand charge transfer (MLCT) transition with a concurrent ligand-centered (LC) transition. At room-temperature, C1 features emission (Φ = 0.04) from its lowest excited states with time constants of 1.2 and 18.3 µs. These lifetimes are assigned to emission processes from the 3MLCT and 3LC state, respectively. This is the first time that a long-lived dual emission has been observed for a ruthenium(II) complex bearing a directly fused extended π-system. Furthermore, the emission of C1 is quenched upon water addition. In contrast to related compounds based on a dipyridophenazine ligand, the excited state energy is not shifted, and the lifetime is drastically decreased to 169 ns.

Unexpected wavelength dependency of the photocatalytic CO2 reduction performance of the well-known (bpy)Re(CO)3Cl complex.

The selective photocatalytic reduction of CO2 to CO has often been accomplished using complexes incorporating the Re(CO)3Cl fragment. We now discovered that the photocatalytic performance of the well-known parent compound (bpy)Re(CO)3Cl (bpy = 2,2'-bipyridine) surprisingly depends on the illumination wavelengths: the turnover numbers (TONs) measured using various cut-off filters showed an increased photocatalytic activity when irradiated with visible light with wavelengths longer than 450 nm - even if the compound hardly absorbs light in this wavelength region. Therefore, catalytic, spectroscopic and theoretical investigations were performed to explain this exceptional effect.

Embedded Multireference Coupled Cluster Theory.

Internally contracted multireference coupled cluster (icMRCC) theory is embedded within multireference perturbation theory (MRPT) to calculate energy differences in large strongly correlated systems. The embedding scheme is based on partitioning the orbital spaces of a complete active space self-consistent field (CASSCF) wave function, with a truncated virtual space constructed by transforming selected projected atomic orbitals (PAOs). MRPT is applied to the environment using a subtractive embedding approach that also allows for multilayer embedding. Benchmark calculations are presented for biradical bond dissociation, spin splitting in a heterocyclic carbene and hydrated Fe(II), and for the super-exchange coupling constant in solid nickel oxide. The method is further applied to two large transition metal complexes with a triple-ζ basis set: an iron complex with 175 atoms and 2939 basis functions, and a nickel complex with 231 atoms, and 4175 basis functions.

Copper Photosensitizers Containing P

Driven by the intention to improve classic heteroleptic copper photosensitizers two novel Cu(I) complexes applying a hetero-bidentate P^N ligand were prepared. A combined photophysical, electrochemical, and theoretical study gives insights into structure-activity relationships and revealed an increased absorptivity. Both complexes were tested for the light-driven production of H2 .