Bobby Happ

2-(1 H-1,2,3-Triazol-4-yl)-Pyridine Ligands as Alternatives to 2,2'-Bipyridines in Ruthenium(II) Complexes

The synthesis of a variety of 2-(1H-1,2,3-triazol-4-yl)-pyridines by click chemistry is demonstrated to provide straightforward access to mono-functionalized ligands. The ring-opening polymerization of epsilon-caprolactone initiated by such a mono-functionalized ligand highlights the synthetic potential of this class of bidentate ligands with respect to polymer chemistry or the attachment onto surfaces and nanoparticles. The coordination to Ru(II) ions results in homoleptic and heteroleptic complexes with the resultant photophysical and electrochemical properties strongly dependent on the number of these ligands attached to the Ru(II) core.

Photoinduced polyaddition of multifunctional azides and alkynes

The photoinduced copper(I)-catalyzed polymerization of multifunctional azides and alkynes is facilitated by the photoreduction of copper(II) acetate generating copper(I) ions without using any additional photoinitiator. The polymerization can only be carried out in solution using at least 15 wt% of methanol. Depending on the catalyst concentration quantitative monomer conversions can be achieved allowing the determination of the mechanical properties. The bifunctional system consisting of a di-azide and di-alkyne exhibited the highest Youngs modulus value of 1600 MPa.

The Self-Healing Potential of Triazole-Pyridine-Based Metallopolymers

The development of artificial self-healing materials represents an emerging and challenging field in material science. Inspired by nature-for instance by the self-healing of mussel byssus threads-metallopolymers gain more and more attention as attractive self-healing materials. These compounds are able to combine the properties of both polymers and metal-ligand interactions. A novel metallopolymer is developed consisting of attached bidentate triazole-pyridine (TRZ-py) ligands and a low glass transition temperature (T g ) lauryl methacrylate backbone. The polymer is cross-linked with different Fe(II) and Co(II) salts. The resulting materials exhibit promising self-healing performance within time intervals of 5.5 to 26.5 h at moderate temperatures of 50 to 100 °C. The materials are characterized by X-ray scattering (SAXS), UV-Vis spectroscopy, and light microscopy.

The radiative decay rates tune the emissive properties of ruthenium(II) polypyridyl complexes: a computational study.

Ru polypyridyl complexes are promising candidates for use as light harvesting antennas in, e.g., artificial photosynthesis, light-driven catalysis, and dye-sensitized solar cells (DSSCs), due to a combination of optimal chemical, electrochemical, and photophysical properties. The rationalization of the photophysical processes, that is, absorption and emission properties and of the excited-state lifetimes of the radiative and nonradiative processes, is fundamental to achieve an optimal behavior of photochemical devices. For instance, to avoid recombination processes in DSSCs and artificial photosynthesis devices, long lifetimes of the excited states of Ru polypyridyl complexes are desired. For the well-known [Ru ACHTUNGTRENNUNG(bpy)3]2+ (bpy= bipyridine) complex, femtosecond transient absorption experiments have shown that, upon excitation to the first singlet excited states (absorption maximum around 450 nm), ultrafast intersystem crossing (ISC) occurs in less than 100 fs, leading to the formation of triplet states with near-unity quantum yield, and hence demonstrated that relaxation processes are dominated by the decay of the triplets rather than by spin-allowed fluorescence from the excited single states. Still, fluorescence bands are often detected and evidence is increasing that intramolecular energy redistribution occurs within the manifold of singlet states, prior to the ISC, as it has been demonstrated for [Fe ACHTUNGTRENNUNG(bpy)3]2+ . Both singlet and triplet excited states have been theoretically assigned as singlet and triplet metal-to-ligand charge transfer states (MLCT and MLCT, respectively) by using time-dependent density functional theory (TD-DFT) calculations. The ultrafast nature of the ISC processes is thus not surprising, as strong spin-orbit couplings (SOC) are expected in states with participation of the metal ion. The MLCT manifold then decays to the lowest triplet excited state because lifetimes of hundreds of nanoseconds are obtained—rates, which, in turn, depend on the sample conditions (i.e. , the solvent and room temperature). In this contribution, we investigate the emissive properties of the heteroleptic Ru polypyridyl complexes shown in Scheme 1 from the computational viewpoint. Both complexes bear two 4,4-dimethyl-2,2’-bipyridine ligands (dmbpy) and a bidentate 2-(1H-1,2,3-triazol-4-yl)pyridine ligand (L). The electron-donating (-OC6H13) or electronwithdrawing (-NO2) peripheral substitution on the phenylACHTUNGTRENNUNGacetylene moiety attached to the ligand L yields complexes 1 and 2, respectively.

Self-Assembly of 3,6-Bis(4-triazolyl)pyridazine Ligands with Copper(I) and Silver(I) Ions: Time-Dependant 2D-NOESY and Ultracentrifuge Measurements

Two 3,6-bis(R-1H-1,2,3-triazol-4-yl)pyridazines (R = mesityl, monodisperse (CH(2)-CH(2)O)(12)CH(3)) were synthesized by the copper(I)-catalyzed azide-alkyne cycloaddition and self-assembled with tetrakis(acetonitrile)copper(I) hexafluorophosphate and silver(I) hexafluoroantimonate in dichloromethane. The obtained copper(I) complexes were characterized in detail by time-dependent 1D [(1)H, (13)C] and 2D [(1)H-NOESY] NMR spectroscopy, elemental analysis, high-resolution ESI-TOF mass spectrometry, and analytical ultracentrifugation. The latter characterization methods, as well as the comparison to analog 3,6-di(2-pyridyl)pyridazine (dppn) systems and their corresponding copper(I) and silver(I) complexes indicated that the herein described 3,6-bis(1H-1,2,3-triazol-4-yl)pyridazine ligands form [2×2] supramolecular grids. However, in the case of the 3,6-bis(1-mesityl-1H-1,2,3-triazol-4-yl)pyridazine ligand, the resultant red-colored copper(I) complex turned out to be metastable in an acetone solution. This behavior in solution was studied by NMR spectroscopy, and it led to the conclusion that the copper(I) complex transforms irreversibly into at least one different metal complex species.

Towards Hydrogen Evolution Initiated by LED Light: 2‐(1H‐1,2,3‐Triazol‐4‐yl)pyridine‐Containing Polymers as Photocatalyst

Two- and three-component polymethacrylates, featuring a 2-(1-substituted-1H-1,2,3-triazol-4-yl)pyridine-based metal complex as photosensitizer, a viologen-type electron mediator, and a triethylene glycol methyl ether as solubilizing part are synthesized by statistical reversible addition-fragmentation chain transfer (RAFT) radical polymerization allowing the construction of well-defined copolymers. Thereby, heteroleptic ruthenium(II) and iridium(III) complexes serve as charged photosensitizers. In hydrogen evolution experiments, as proof-of-concept, triethylamine is utilized as a sacrificial donor and colloidal platinum as hydrogen evolving catalyst. The macromolecules bearing heteroleptic iridium(III) complexes of the general formula [Ir(ppy)2 (trzpy)]PF6 (ppy: 2-phenylpyridine; trzpy: 2-(1-substituted-1H-1,2,3-triazol-4-yl)pyridine) and [Ir(btac)2 (trzpy)]PF6 (btac: 3-(2-benzothiazolyl)-7-(diethylamino)coumarin) are photocatalytically active producing molecular hydrogen in water upon illumination at 470 nm. By changing the cyclometalating ligand from ppy to btac, the photocatalytic performance of the copolymer as reflected in the turnover number increases by two orders of magnitude.

Incorporation of core–shell particles into methacrylate based composites for improvement of the mechanical properties

The fracture toughness of polymeric materials and composites can be enhanced by the incorporation of polymer nanoparticles. The combination of a soft core and a hard shell leads to an improvement of the fracture toughness of the polymeric composites. Thereby, the mechanical resistance of the materials is commonly decreased. In our approach, core–shell nanoparticles consisting of an ethylene glycol dimethacrylate (EGDMA) crosslinked poly(butyl acrylate) (PBA) core and a poly(methyl methacrylate) (PMMA) shell were synthesized. The polymer particles were incorporated into triethylene glycol dimethacrylate (TEGDMA)/urethane dimethacrylate (UDMA) based composites in order to tune the mechanical properties. Different core–shell ratios were applied to study the influence on the fracture toughness and E-modulus. An examination of shell-crosslinking with a TEGDMA content of up to 8% was performed to improve particle stability and dispersibility. The particle sizes and morphologies were characterized by dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM) and analytical ultracentrifugation (AUC). Latex particle sizes of 70 to 220 nm were obtained. The mechanical properties (flexural strength, E-modulus and K1c) of polymer composites were investigated in three-point bending tests. Core/shell ratios of 50/50 showed a decreasing effect on flexural strength, E-modulus and K1c. Polymer particles with core/shell ratios of 30/70 led to a significant increase of the mechanical properties with maxima of 1.206 MPa m1/2 (K1c) (increase of 65%), E-modulus of 1.90 GPa (increase of 18%) and flexural strength of 79 MPa (increase of 18%). This study represents the first report of a simultaneous improvement of fracture toughness and E-modulus (at the same time) of additive filled polymer composites. The improvement of mechanical properties makes these materials interesting as tougheners for hard tissue applications like bone cements or dental replacement materials.

2-[1-(1-Naphth-yl)-1H-1,2,3-triazol-4-yl]pyridine.

In the crystal structure of the title compound, C17H12N4, the angle between the naphthalene and 1H-1,2,3-triazole ring systems is 71.02 (4)° and that between the pyridine and triazole rings is 8.30 (9)°.