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.

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.

Photogenerated avenues in macromolecules containing Re(I), Ru(II), Os(II), and Ir(III) metal complexes of pyridine-based ligands.

Pyridine-based ligands, such as 2,2'-bipyridine and 1,10-phenanthroline, have gained much interest in the fields of supramolecular chemistry as well as materials science. The appealing optoelectronic properties of their complexes with heavy d(6) transition metal ions, such as Ru(ii), Os(II), Re(I) and Ir(III), primarily based on the metal-to-ligand charge-transfer (MLCT) nature featuring access to charge-separated states, have provided the starting point for many studies in the field of dye-sensitized solar cells (DSSCs), organic light emitting diodes (OLEDs), artificial photosynthesis and photogenerated electron as well as energy transfer processes. This critical review provides a comprehensive survey over central advances in the field of soluble metal-containing macromolecules in the last few decades. The synthesis and properties of functionalized 2,2'-bipyridyine- and 1,10-phenanthroline-based d(6) metal complexes, in particular, their introduction into different prevailing polymeric structures are highlighted. In the most part of the review metal complexes which have been attached as pendant groups on the polymer side chain are covered. Selected applications of the herein discussed metal-containing macromolecules are addressed, particularly, with respect to photogenerated electron/energy transfer processes. In order to enable a deeper understanding of the properties of the ligands and metal complexes, the fundamentals of selected photophysical processes will be discussed (223 references).

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.

N-heterocyclic donor- and acceptor-type ligands based on 2-(1H-[1,2,3]triazol-4-yl)pyridines and their ruthenium(II) complexes.

New 2-(1H-[1,2,3]triazol-4-yl)pyridine bidentate ligands were synthesized as bipyridine analogs, whereas different phenylacetylene moieties of donor and acceptor nature were attached at the 5-position of the pyridine unit. The latter moieties featured a crucial influence on the electronic properties of those ligands. The N-heterocyclic ligands were coordinated to ruthenium(II) metal ions by using a bis(4,4'-dimethyl-2,2'-bipyridine)ruthenium(II) precursor. The donor or acceptor capability of the 2-(1H-[1,2,3]triazol-4-yl)pyridine ligands determined the quantum yield of the resulting ruthenium(II) complexes remarkably. Separately, 2-([1,2,3]triazol-4-yl)pyridine ligands are known to be potential quenchers, but using these new ligand systems led to room temperature emission of the corresponding ruthenium(II) complexes. The compounds have been fully characterized by elemental analysis, high-resolution ESI mass spectrometry, (1)H and (13)C NMR spectroscopy, and X-ray crystallography. Theoretical calculations for two ruthenium(II) complexes bearing a donor and acceptor unit, respectively, were performed to gain a deeper understanding of the photophysical behavior.

2-(1H-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.

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

In the crystal structure of the title compound, C(17)H(12)N(4), 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)°.