Aggregation Game: Changing Solid-State Emission Using Different Counterions in Monoalkynylphosphonium Pt(II) Complexes.

Two series of heteroleptic monoalkynylphosphonium Pt(II) complexes decorated with 2,2':6',2''-terpyridine (, series) and 6-phenyl-2,2'-bipyridine (, series) ligands, were prepared and characterized by spectroscopic methods. The complexes obtained exhibit triplet emission in solution, and the characteristics inside the series depend on the nature of the alkynylphosphonium ligand. The description of electronic transitions responsible for energy absorption and emission in discrete Pt(II) complexes was made on the basis of a detailed analysis of the results of DFT calculations, and has shown to involve MLCT, ILCT, and LLCT transitions.

Azaindolizine proton cranes attached to 7-hydroxyquinoline and 3-hydroxypyridine: a comparative theoretical study.

Theoretical design of several proton cranes, based on 7-hydroxyquinoline and 3-hydroxypyridine as proton-transfer frames, has been attempted using ground and excited-state density functional theory (DFT) calculations in various environments. Imidazo[1,2-]pyridine, pyrazolo[1,5-]pyridine and benzimidazole were considered as proton crane units. The proton crane action requires the existence of a single enol-like form in the ground state, which under excitation goes to the end keto-like one through a series of consecutive excited-state intramolecular proton transfers (ESIPT) and twisting steps with the participation of a crane unit, resulting in a long-range intramolecular proton transfer.

Theoretical Understanding of the Long-Range Proton Transfer Mechanism in 7-Hydroxy Quinoline-Based Molecular Switches: Varma's Proton Crane and Its Analogues.

Herein, the detailed mechanism of intramolecular proton transfer in molecular switches, constructed from 7-hydroxy quinoline substituted in the eight-position C-C single axle, connected to three different proton cranes (morpholine, piperidine, and 1,3,5-dioxazine), was investigated by means of theoretical chemistry. The theoretical interpretation of the rotational mechanism and its stable structures were proposed for the well-known Varma's proton crane, based on morpholine molecule. The reliability of the theoretical simulations was confirmed by the available literature data from time-dependent IR measurements.

Alkynylphosphonium Pt(II) Complexes: Synthesis, Characterization, and Features of Photophysical Properties in Solution and in the Solid State.

A series of heteroleptic bis-alkynyl-diimine mononuclear Pt(II) complexes with alkynylphosphonium and di--butyl-2,2'-bipyridine (dtbpy) ligands have been prepared and characterized by spectroscopic methods and single-crystal XRD. The Pt(II) complexes obtained in the present study demonstrate triplet emission in solution, which originates from MLCT/LC states where the nature of the π-conjugated linker in the alkynylphosphonium ligand manages the contributions of each transition, and this conclusion is supported by DFT calculations. Additionally, the presence of the phosphonium group connected to alkynyl through the π-conjugated linker enhances nonlinear optical properties of the Pt(II) complexes increasing two-photon absorption cross section up to 400 GM.

Favipiravir-Tautomeric and Complexation Properties in Solution.

The tautomeric properties of favipiravir were investigated experimentally for the first time by using molecular spectroscopy (UV-Vis absorption, fluorescence and NMR), as well as DFT quantum-chemical calculations. According to the obtained results, the enol tautomer is substantially more stable in most of the organic solvents. In the presence of water, a keto form appears to be favored due to the specific solute-solvent interactions.

Controllable Synthesis and Luminescence Behavior of Tetrahedral Au@Cu and Au@Ag Clusters Supported by tris(2-Pyridyl)phosphine.

We report herein a family of polynuclear complexes, [Au@Ag(PyP)]X and [Au@Cu(PyP)]X [X = NO, ClO, OTf, BF, SbF], containing unprecedented Au-centered Ag and Cu tetrahedral cores supported by tris(2-pyridyl)phosphine (PyP) ligands. The [Au@Ag] clusters are synthesized controlled substitution of the central Ag(I) ion in all-silver [Ag@Ag] precursors by the reaction with Au()Cl, while the [Au@Cu] cluster is assembled through the treatment of a pre-organized [Au(PyP)] metallo-ligand with 4 equiv of a Cu(I) source. The structure of the Au@M clusters has been experimentally and theoretically investigated to reveal very weak intermolecular Au-M metallophilic interactions.

The Tail Wags the Dog: The Far Periphery of the Coordination Environment Manipulates the Photophysical Properties of Heteroleptic Cu(I) Complexes.

In this work we show, using the example of a series of [Cu(Xantphos)(N^N)] complexes (N^N being substituted 5-phenyl-bipyridine) with different peripheral N^N ligands, that substituents distant from the main action zone can have a significant effect on the physicochemical properties of the system. By using the C≡C bond on the periphery of the coordination environment, three hybrid molecular systems with -Si(CH), -Au(PR), and -CHN(CH)CH fragments were produced. The Cu(I) complexes thus obtained demonstrate complicated emission behaviour, which was investigated by spectroscopic, electrochemical, and computational methods in order to understand the mechanism of energy transfer.

Just Add the Gold: Aggregation-Induced-Emission Properties of Alkynylphosphinegold(I) Complexes Functionalized with Phenylene-Terpyridine Subunits.

A series of organometallic complexes containing an alkynylphosphinegold(I) fragment and a phenylene-terpyridine moiety connected together by flexible linker have been prepared using the specially designed terpyridine ligands. The compounds were studied crystallographically to reveal that all of them contain a linearly coordinated Au(I) atom and a free terpyridine moiety. The different orientations of the molecules relative to each other in the solid state determine the multiple noncovalent interactions such as antiparallel ππ stacking, CH-π, and CH-Au, but no aurophilic interactions are realized.

Self-catalytic mechanism of prebiotic reactions: from formamide to pterins and guanine.

Reaction pathway of prebiotic reactions for formation of the pteridines: pterin, xanthopterine, isoxanthopterine and leucopterine, as well as the purine nucleobase guanine from pure formamide are presented. In these reactions, formamide or its tautomer, formimidic acid, play the role of proton-carrying catalyst. All required raw materials, such as hydrogen cyanide, ammonia, water, formic acid, urea, 2-aminomalononitrile, glyoxal, glyoxylic acid and oxalic acid needed in the self-catalyzed reactions are obtained by partial decomposition of formamide.

Chemical evolution: from formamide to nucleobases and amino acids without the presence of catalyst.

Abiotic synthesis of nucleobases and amino acids is of critical importance as it sheds light on potential prebiotic chemical reactions. During thermal decomposition of formamide in vacuum conditions, purine, cytosine, adenine, hypoxanthine, uracil, pterin, urea, urocanic acid, glycine, alanine and norvaline were detected. The compounds were obtained without catalyst by heating at 100-180 °C or microwave heating of formamide.