Emissive Ruthenium-Bisdiimine Complexes with Chelated Thioether Donors
Journal article, 2016
The photophysical properties of ruthenium(II) complexes of bidentate 2-[(alkylthio)methyl]pyridine (N,S) ligands have been systematically investigated. The co-ligands in the heteroleptic complexes were diimines (N,N ligands, e.g., bpy, phen) or tripodal tetradentate tris(2-pyridylmethyl)amine (tpa). Their X-ray structures revealed little variation in the Ru-S (2.31-2.33 angstrom) and Ru-N (2.06-2.11 angstrom) bond lengths. Despite this, considerable variation can be observed in the electrochemistry and spectroscopy measurements. The presence of the thioether sulfur donor results in a shift to a more positive potential of the Ru2+/Ru3+ process, and the absorption maxima are consequently blueshifted in [Ru(N,N)(2)(N,S)](2+) complexes compared with the [Ru(N,N)(3)](2+) analogues. The [Ru(N,N)(2)(N,S)](2+) complexes display strong room-temperature emission from (MLCT)-M-3 states, governed by the N,N donors. This is corroborated by low-temperature steady-state emission studies, which revealed typical (MLCT)-M-3 emission profiles and excited-state lifetimes of around 5-10 mu s.