Rationalizing the molecular origins of Ru- and Fe-based dyes for dye-sensitized solar cells

Structure-based biological investigations on ruthenium complexes containing 2,2'-bipyridine ligands and their applications in photodynamic therapy as a potential photosensitizer

Ruthenium complexes have been investigated for various biological applications by virtue of their radical scavenging, DNA binding, receptor binding, and cytotoxic abilities; especially the possible potential application of these complexes in photodynamic therapy (PDT). This study focuses on the synthesis, structural characterization and biological application (pertaining to its cytotoxicity and radical generation) of ruthenium complexed with salicylaldehyde fumaryl-dihydrazone (slfhH4 ), salicylaldehyde glutaryl-di-hydrazone (slfgH4 ) and 2,2'-bipyridine (bpy). During the synthesis, the anticipated complex was precipitated out but as serendipity, Ruthenium(II) tris (2,2'-bipyridyl) monochloride nonahydrate {[Ru(bpy)3 ]2+ .Cl.9H2 O} (RBMN) and Ruthenium(II) tris (2,2'-bipyridyl) monochloride septahydrate {[Ru(bpy)3 ]2+ .Cl.7H2 O}(RBMS) were crystallized from the filtrate. The crystal structure of complexes RBMN and RBMS were determined by a single-crystal X-ray diffraction methods and it showed that chlorine anion lies at the crystallographic axis and forms a halogen hydrogen-bonded organic framework (XHOF) to provide the stability. In comparison with similar structures in Cambridge Crystallographic Data Center (CCDC) revealed that the nature of the XHOF framework and the layered packing are conserved. The compounds showed excellent cytotoxic ability (against L6 cells) and the nitro blue tetrazolium (NBT) assay upon irradiation to light revealed its ability to produce reactive oxygen species (ROS). The presence of partially occupied water molecules in the layered organization within the crystal packing mimics the release of ROS resulting in cytotoxicity. The structural results together with the biological data make these complexes interesting candidates for potential photosensitizers for PDT applications.

Triboluminescence Phenomenon Based on the Metal Complex Compounds-A Short Review

Triboluminescence (TL) is a phenomenon of light emission resulting from the mechanical force applied to a substance. Although TL has been observed for many ages, the radiation mechanism is still under investigation. One of the exemplary compounds which possesses triboluminescent properties are copper(I) thiocyanate bipyridine triphenylphosphine complex [Cu(NCS)(py)₂(PPh₃)], europium tetrakis dibenzoylmethide triethylammonium EuD₄TEA, tris(bipyridine)ruthenium(II) chloride [Ru(bpy)₃]Cl₂, and bis(triphenylphosphine oxide)manganese(II) bromide Mn(Ph₃PO)₂Br₂. Due to the effortless synthesis route and distinct photo- and triboluminescent properties, these compounds may be useful model substances for the research on the triboluminescence mechanism. The advance of TL studies may lead to the development of a new group of sensors based on force-responsive (mechanical stimuli) materials. This review constitutes a comprehensive theoretical study containing available information about the coordination of metal complex synthesis methodologies with their physical, chemical, and spectroscopic properties.

Electrolyte/Dye/TiO2 Interfacial Structures of Dye-Sensitized Solar Cells Revealed by In Situ Neutron Reflectometry with Contrast Matching

The nature of an interfacial structure buried within a device assembly is often critical to its function. For example, the dye/TiO₂ interfacial structure that comprises the working electrode of a dye-sensitized solar cell (DSC) governs its photovoltaic output. These structures have been determined outside of the DSC device, using ex situ characterization methods; yet, they really should be probed while held within a DSC since they are modulated by the device environment. Dye/TiO₂ structures will be particularly influenced by a layer of electrolyte ions that lies above the dye self-assembly. We show that electrolyte/dye/TiO₂ interfacial structures can be resolved using in situ neutron reflectometry with contrast matching. We find that electrolyte constituents ingress into the self-assembled monolayer of dye molecules that anchor onto TiO₂. Some dye/TiO₂ anchoring configurations are modulated by the formation of electrolyte/dye intermolecular interactions. These electrolyte-influencing structural changes will affect dye-regeneration and electron-injection DSC operational processes. This underpins the importance of this in situ structural determination of electrolyte/dye/TiO₂ interfaces within representative DSC device environments.

Structural, electrochemical and photophysical behavior of Ru(ii) complexes with large bite angle sulfur-bridged terpyridyl ligands

Sulfur-bridged terpyridyl ligands expand the bite angles in Ru(ii) species leading to geometries very close to that of a “perfect” octahedron. Altering the donor strength of substituents results in systematic tuning of the redox properties.

Encapsulation of the [Ru(bpy)3]2+ luminophore in a unique hydrogen-bonded host framework

One-dimensional networks of the well-known photosensitizer [Ru(bpy)₃]²⁺ are encapsulated in an unusual hydrogen-bonded crystalline host framework.

A Million Crystal Structures: The Whole Is Greater than the Sum of Its Parts

The founding in 1965 of what is now called the Cambridge Structural Database (CSD) has reaped dividends in numerous and diverse areas of chemical research. Each of the million or so crystal structures in the database was solved for its own particular reason, but collected together, the structures can be reused to address a multitude of new problems. In this Review, which is focused mainly on the last 10 years, we chronicle the contribution of the CSD to research into molecular geometries, molecular interactions, and molecular assemblies and demonstrate its value in the design of biologically active molecules and the solid forms in which they are delivered. Its potential in other commercially relevant areas is described, including gas storage and delivery, thin films, and (opto)electronics. The CSD also aids the solution of new crystal structures. Because no scientific instrument is without shortcomings, the limitations of CSD research are assessed. We emphasize the importance of maintaining database quality: notwithstanding the arrival of big data and machine learning, it remains perilous to ignore the principle of garbage in, garbage out. Finally, we explain why the CSD must evolve with the world around it to ensure it remains fit for purpose in the years ahead.

Discovery of S···C≡N Intramolecular Bonding in a Thiophenylcyanoacrylate-Based Dye: Realizing Charge Transfer Pathways and Dye···TiO2 Anchoring Characteristics for Dye-Sensitized Solar Cells

Donor-π-acceptor dyes containing thiophenyl π-conjugated units and cyanoacrylate acceptor groups are among the best-performing organic chromophores used in dye-sensitized solar cell (DSC) applications. Yet, the molecular origins of their high photovoltaic output have remained unclear until now. This synchrotron-based X-ray diffraction study elucidates these origins for the high-performance thiophenylcyanoacrylate-based dye MK-2 (7.7% DSC device efficiency) and its molecular building block, MK-44. The crystal structures of MK-2 and MK-44 are both determined, while a high-resolution charge-density mapping of the smaller molecule was also possible, enabling the nature of its bonding to be detailed. A strong S···C≡N intramolecular interaction is discovered, which bears a bond critical point, thus proving that this interaction should be formally classified as a chemical bond. A topological analysis of the π-conjugated portion of MK-44 shows that this S···C≡N bonding underpins the highly efficient intramolecular charge transfer (ICT) in thiophenylcyanoacrylate dyes. This manifests as two bipartite ICT pathways bearing carboxylate and nitrile end points. In turn, these pathways dictate a preferred COO/CN anchoring mode for the dye as it adsorbs onto TiO₂ surfaces, to form the dye···TiO₂ interface that constitutes the DSC working electrode. These results corroborate a recent proposal that all cyanoacrylate groups anchor onto TiO₂ in this COO/CN binding configuration. Conformational analysis of the MK-44 and MK-2 crystal structures reveals that this S···C≡N bonding will persist in MK-2. Accordingly, this newly discovered bond affords a rational explanation for the attractive photovoltaic properties of MK-2. More generally, this study provides the first unequivocal evidence for an S···C≡N interaction, confirming previous speculative assignments of such interactions in other compounds.

A Simple Approach for Predicting the Spin State of Homoleptic Fe(II) Tris-diimine Complexes

We propose a simple method for predicting the spin state of homoleptic complexes of the Fe(II) d⁶ ion with chelating diimine ligands. The approach is based on the analysis of a single metric parameter within a free (noncoordinated) ligand: the interatomic separation between the N-donor metal-binding sites. An extensive analysis of existing complexes allows the determination of critical N···N distances that dictate the regions of stability for the high-spin and low-spin complexes, as well as the intermediate range in which the magnetic bistability (spin crossover) can be observed. The prediction has been tested on several complexes that demonstrate the validity of our method.

Low-dimensional compounds containing cyanide groups. XXV. Synthesis, spectroscopic properties and crystal structures of two ionic iron(II) complexes with tricyanomethanide: tris(1,10-phenanthroline-κ(2)N,N')iron(II) bis(tricyanomethanide) and tris(2,2'-bipyridine-κ(2)N,N')iron(II) bis(tricyanomethanide) sesquihydrate

Two new diamagnetic coordination compounds, [Fe(phen)3][C(CN)3]2, (I), and [Fe(bpy)3][C(CN)3]2·1.5H2O, (II), have been synthesized and characterized by single-crystal X-ray diffraction analysis, and IR and UV-Vis spectroscopy (phen is 1,10-phenanthroline, C12H8N2, and bpy is 2,2'-bipyridine, C10H8N2). Both compounds are ionic with distorted octahedral [Fe(phen)3](2+) or [Fe(bpy)3](2+) complex cations, with average Fe-N distances of 1.977 (2) and 1.971 (3) Å, respectively, and two uncoordinated planar tricyanomethanide, or [C(CN)3](-), counter-anions balancing the positive charges of the cations. Solvent water molecules and tcm anions in (II) are linked via O-H...N hydrogen bonds into negatively charged layers and the interlayer space is filled by [Fe(bpy)3](2+) cations. The structures of (I) and (II) are stabilized by π-π interactions between the stacked aromatic rings of the phen ligands of two adjacent cations and by O-H...N hydrogen bonds, respectively, and also by π-π stacking interactions between phen and tcm units in (I).