Synthesis, crystal structure, electrochemical properties, and photophysical characterization of ruthenium(II) 4,4′-dimethoxy-2,2′-bipyridine polypyridine complexes

A series of ruthenium(II) polypyridine complexes of the type [Ru(tpy)((CH3O)(2)bpy)(4-R-py)](2+), where tpy = 2,2 ';6 ',2 ''-terpyridine, (CH3O)(2)bpy = 4,4 '-dimethoxy-2,2 '-bipyridine, and 4-R-py = pyridine (py, 2), 4-methoxypyridine (4-CH3O-py, 3), 4-aminopyridine (4-NH2-py, 4), were synthesized and their crystal structures, electronic absorption, luminescence, and electrochemical properties were investigated. The effect of adding electron-donating groups to the bidentate and monodentate ligand was investigated and compared with [Ru(tpy)(bpy)(py)](2+) (1) where bpy = 2,2 '-bipyridine. While anticipated trends were not observed for the Ru-N(6) bond length as 4-R-py was varied, noticeable modifications of the measured photophysical properties were observed. A red-shift of the metal-to-ligand charge transfer ((MLCT)-M-1) is observed from 466 nm in 1 to 474 nm, 478 nm, and 485 nm for 2-4, respectively. Additionally, a red-shift in the luminescence maxima is observed in 2-4 as compared to 1, with 4 exhibiting the greatest shift of more than 100 nm. Complexes 2-4 exhibited luminescence quantum yields of 2.7 x 10(-4), 7.2 x 10(-4), and 7.4 x 10(-4), respectively, which are increased compared to the quantum yield of 2.0 x 10(-4) in 1. These findings demonstrate systematic tuning of absorbance and luminescence properties of ruthenium polypyridine complexes by addition of pi-donating substituents to the monodentate and bidentate ligand.

Automated summary

The absorption and luminescence properties of ruthenium polypyridine complexes can be systematically tuned by adding electron-donating substituents to the ligands. While the anticipated trend in the Ru-N(6) bond length was not observed, noticeable modifications in the measured photophysical properties were observed.