A Combined Spectroscopic and Theoretical Study on a Ruthenium Complex Featuring a π-Extended dppz Ligand for Light-Driven Accumulation of Multiple Reducing Equivalents.

The 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 π-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.

Tuning the Electron Storage Potential of a Charge-Photoaccumulating RuII Complex by a DFT-Guided Approach.

Molecular photosensitizers that are able to store multiple reducing equivalents are of great interest in the field of solar fuel production, where most reactions involve multielectronic reduction processes. In order to increase the reducing power of a ruthenium tris-diimine charge-photoaccumulating complex, two structural modifications on its fused dipyridophenazine-pyridoquinolinone ligand were computationally investigated. Addition of an electron-donating oxime group was calculated to substantially decrease the reduction potentials of the complex, thus guiding the synthesis of a pyridoquinolinone-oxime derivative. Its spectroscopic and (spectro)electrochemical characterization experimentally confirmed the DFT predictions, with the first and second reduction processes cathodically shifted by -0.24 and -0.14 V, respectively, compared to the parent complex. Moreover, the ability of this novel artificial photosynthetic system to store two photogenerated electrons at a more reducing potential, via a proton-coupled electron-transfer mechanism, was demonstrated.

Recent Advances in Isoindigo-Inspired Organic Semiconductors.

Over the past decade, isoindigo has become a widely used electron-deficient subunit in donor-acceptor organic semiconductors, and these isoindigo-based materials have been widely used in both organic photovoltaic (OPV) devices and organic field effect transistors (OFETs). Shortly after the development of isoindigo-based semiconductors, researchers began to modify the isoindigo structure in order to change the optoelectronic properties of the resulting materials. This led to the development of many new isoindigo-inspired compounds; since 2012, the Kelly Research Group has synthesized a number of these isoindigo analogues and produced a variety of new donor-acceptor semiconductors. In this Personal Account, recent progress in the field is reviewed. We describe how the field has evolved from relatively simple donor-acceptor small molecules to structurally complex, highly planarized polymer systems. The relevance of these materials in OPV and OFET applications is highlighted, with particular emphasis on structure-property relationships.

Lewis Acid-Base Chemistry of 7-Azaisoindigo-Based Organic Semiconductors.

Low-band-gap organic semiconductors are important in a variety of organic electronics applications, such as organic photovoltaic devices, photodetectors, and field effect transistors. Building on our previous work, which introduced 7-azaisoindigo as an electron-deficient building block for the synthesis of donor-acceptor organic semiconductors, we demonstrate how Lewis acids can be used to further tune the energies of the frontier molecular orbitals. Coordination of a Lewis acid to the pyridinic nitrogen of 7-azaisoindigo greatly diminishes the electron density in the azaisoindigo π-system, resulting in a substantial reduction in the lowest unoccupied molecular orbital (LUMO) energy. This results in a smaller highest occupied molecular orbital-LUMO gap and shifts the lowest-energy electronic transition well into the near-infrared region. Both H+ and BF3 are shown to coordinate to azaisoindigo and affect the energy of the S0 → S1 transition. A combination of time-dependent density functional theory and UV/vis and 1H NMR spectroscopic titrations reveal that when two azaisoindigo groups are present and high concentrations of acid are used, both pyridinic nitrogens bind Lewis acids. Importantly, we demonstrate that this acid-base chemistry can be carried out at the solid-vapor interface by exposing thin films of aza-substituted organic semiconductors to vapor-phase BF3·Et2O. This suggests the possibility of using the BF3-bound 7-azaisoindigo-based semiconductors as n-type materials in various organic electronic applications.

Self-assembled Ln(III)4 (Ln = Eu, Gd, Dy, Ho, Yb) [2 × 2] square grids: a new class of lanthanide cluster.

Self-assembly of the Ln(III) ions (Ln = Eu, Gd, Dy, Ho, Yb) into square [2 × 2] grid-like arrays has been readily effected using simple, symmetric ditopic ligands based on a carbohydrazone core. The metal ions are connected via single atom bridges (e.g., µ2-O(hydrazone), µ2-OH, µ2-OMe, µ2-1,1-N3(-), µ4-O), depending on reaction conditions. The Gd(III)4 examples exhibit intramolecular antiferromagnetic exchange (-J < 0.11 cm(-1)), and in one Dy(III)4 example, with a combination of µ2-1,1-N3(-), and µ4-O bridges linking adjacent metal ions, SMM behavior is observed. One thermally driven relaxation process is observed in the temperature range 10-25 K (τ0 = 6.5(1) × 10(-7) s, U(eff) = 110(1) K) in the presence of an 1800 Oe external field, employed to suppress a second quantum based relaxation process. The extended group of Ln(III) ions which submit to this controlled self-assembly, typical of the transition metal ions, indicates the general applicability of this approach to the lanthanides. This occurs despite the anticipated limitations based on larger ionic radii and coordination numbers, and is an encouraging sign for extension to larger grids with appropriately chosen polytopic ligands.

6,6'-Dimeth-oxy-2,2'-{[(E,E)-hydrazine-1,2-diyl-idene]bis-(methanylyl-idene)}diphenol methanol disolvate.

The title compound, C(16)H(16)N(2)O(4)·2CH(3)OH, is a hydrazone in an E geometric arrangement, with an inversion centre at the mid-point of the N-N bond. A symmetry-related pair of six-membered hydrogen-bonded rings [graph-set motif S(1) (1)(6)] are present for the terminal vanillin-imine moieties. Two lattice methanol solvent mol-ecules are present per formula unit (Z' = 1/2), which form hydrogen-bonded chains along [010] with two orientations due to disorder of the methanol H-atom.

Primary fragmentation pathways of gas phase [M(uracil-H)(uracil)]+ complexes (M=Zn, Cu, Ni, Co, Fe, Mn, Cd, Pd , Mg, Ca, Sr, Ba, and Pb): loss of uracil versus HNCO.

Complexes formed between metal dications, the conjugate base of uracil, and uracil are investigated by sustained off-resonance irradiation collision-induced dissociation (SORI-CID) in a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. Positive-ion electrospray spectra show that [M(Ura-H)(Ura)](+) (M=Zn, Cu, Ni, Co, Fe, Mn, Cd, Pd, Mg, Ca, Sr, Ba, or Pb) is the most abundant ion even at low concentrations of uracil. SORI-CID experiments show that the main primary decomposition pathway for all [M(Ura-H)(Ura)](+) , except where M=Ca, Sr, Ba, or Pb, is the loss of HNCO. Under the same SORI-CID conditions, when M is Ca, Sr, Ba, or Pb, [M(Ura-H)(Ura)](+) are shown to lose a molecule of uracil. Similar results were observed under infrared multiple-photon dissociation excitation conditions, except that [Ca(Ura-H)(Ura)](+) was found to lose HNCO as the primary fragmentation product. The binding energies between neutral uracil and [M(Ura-H)](+) (M=Zn, Cu, Ni, Fe, Cd, Pd ,Mg, Ca, Sr Ba, or Pb) are calculated by means of electronic-structure calculations. The differences in the uracil binding energies between complexes which lose uracil and those which lose HNCO are consistent with the experimentally observed differences in fragmentation pathways. A size dependence in the binding energies suggests that the interaction between uracil and [M(Ura-H)](+) is ion-dipole complexation and the experimental evidence presented supports this.