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'-dimethy1-2,2'-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(11) complexes remarkably. Separately, 2-([1,2,3]triazol-4-yppyridine ligands are known to be potential quenchers, but using these new ligand systems led to room temperature emission of the corresponding ruthenium(I I) complexes. The compounds have been fully characterized by elemental analysis, high-resolution ESI mass spectrometry, H-1 and C-13 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.